tox 4.36.0 started enforcing the constraint that a `package_env`
environemnt only installs what is listed in `build-system.requires`. We
use `pypa/build` to build the wheel from the sdist instead of building
the wheel directly. `pypa/build` is an external command so it was not
listed in `build-system/requires` and was just listed as an extra tox
environemnt dependency. Now listing an extra dependency is not allowed
so we just list `pypa/build` under `build-system.requires` until a
cleaner solution is found.

See tox-dev/tox#3687 (comment)

tox 4.36.0 started enforcing the constraint that a `package_env`
environemnt only installs what is listed in `build-system.requires`. We
use `pypa/build` to build the wheel from the sdist instead of building
the wheel directly. `pypa/build` is used as an external command so it
was not listed in `build-system/requires` and was just listed as an
extra tox environemnt dependency. Now listing an extra dependency is not
allowed so we install `pypa/build` in the packaging environment's
commands until a cleaner solution is found.

See tox-dev/tox#3687 (comment)

PR #3687 (fix for #3412) added a hard Fail in
Pep517VenvPackager._setup_env() that rejects any deps on PEP-517
packaging environments. This broke two downstream consumers:

tox-uv — Tests for editable-legacy, workspace, and no_pyproject
scenarios set deps = wheel on .pkg because uv doesn't seed wheel into
venvs by default (unlike virtualenv). The editable-legacy flow needs
wheel importable in the packaging venv for setup.py develop. CI:
https://github.com/tox-dev/tox-uv/actions/runs/22071221669

Uses package = external with deps = build on .pkg to run python -m build
for sdist→wheel workflow. Discussion:
#3491 (reply in thread)
Fix PR: qiskit-community/qiskit-experiments#1615


Only raise the error when call_require_hooks is a subset of {"sdist",
"wheel", "editable"} (standard PEP-517 types). Allow deps when
editable-legacy or external is involved

Fixes: #3731

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- [x] ran the linter to address style issues (`tox -e fix`)
- [x] wrote descriptive pull request text
- [x] ensured there are test(s) validating the fix
- [x] added news fragment in `docs/changelog` folder
- [ ] updated/extended the documentation

---------

Co-authored-by: Bernát Gábor <gaborjbernat@gmail.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

tox 4.36.0 started enforcing the constraint that a `package_env`
environment only installs what is listed in `build-system.requires`. We
use `pypa/build` to build the wheel from the sdist instead of building
the wheel directly. `pypa/build` is used as an external command so it
was not listed in `build-system/requires` and was just listed as an
extra tox environment dependency. Now listing an extra dependency is not
allowed so we install `pypa/build` in the packaging environment's
commands until a cleaner solution is found.

See tox-dev/tox#3687 (comment)

Additionally, a pylint disable comment was added to `numpy.finfo.eps`
since
this was also needed for the CI to pass.

tox 4.36.0 started enforcing the constraint that a `package_env`
environment only installs what is listed in `build-system.requires`. We
use `pypa/build` to build the wheel from the sdist instead of building
the wheel directly. `pypa/build` is used as an external command so it
was not listed in `build-system/requires` and was just listed as an
extra tox environment dependency. Now listing an extra dependency is not
allowed so we install `pypa/build` in the packaging environment's
commands until a cleaner solution is found.

See tox-dev/tox#3687 (comment)

Additionally, a pylint disable comment was added to `numpy.finfo.eps`
since
this was also needed for the CI to pass.

tox 4.36.0 started enforcing the constraint that a `package_env`
environment only installs what is listed in `build-system.requires`. We
use `pypa/build` to build the wheel from the sdist instead of building
the wheel directly. `pypa/build` is used as an external command so it
was not listed in `build-system/requires` and was just listed as an
extra tox environment dependency. Now listing an extra dependency is not
allowed so we install `pypa/build` in the packaging environment's
commands until a cleaner solution is found.

See tox-dev/tox#3687 (comment)

Additionally:

* A pylint disable comment was added to `numpy.finfo.eps` since 
  this was also needed for the CI to pass.
* testtools 2.8.3 was excluded from the test dependencies to avoid
  incompatibility with stestr. The hope is the next release of stestr or
  testtools will address the incompatibility. See:
  testing-cabal/testtools#566

This change started as a fix for a change in behavior in tox but evolved
into
a set of three unrelated small fixes that are all needed to get the CI
to pass
again:

* Set a minimum version for `tox` of 4.38.0 so that we pick up
  tox-dev/tox#3730 which addresses
  tox-dev/tox#3687 (comment).
Additionally, `tox-uv` is added as a tox dependency for consistency
since
that is used in CI (but actually set it to !=4.36,!=4.37 since 4.38.0
requires
  Python >=3.10 and this change is a precursor to the one that drops
  Python 3.9).
* A pylint disable comment was added to `numpy.finfo.eps` since 
  this was also needed for the CI to pass.
* testtools 2.8.3 was excluded from the test dependencies to avoid
  incompatibility with stestr. The hope is the next release of stestr or
  testtools will address the incompatibility. See:
  testing-cabal/testtools#566