…dev#3891)

Running `tox -e py314t` builds the wheel in a `.pkg` environment that
may use non-free-threaded Python. The `default_wheel_tag` function only
compared `version_no_dot` and `impl_lower` between the package env and
target env. Since `version_no_dot` is `"314"` for both `py314` and
`py314t`, they shared the same `.pkg` environment, producing wheels with
`cp314` tags instead of `cp314t`. 🐛 `pip install` in the free-threaded
target env then rejects the wheel as unsupported.

The fix adds `free_threaded` to the compatibility check in
`default_wheel_tag()` and appends the `t` suffix to the generated
environment name when the target interpreter is free-threaded (e.g.,
`.pkg-cpython314t`). This ensures each threading variant gets its own
build environment with matching wheel tags.

Fixes tox-dev#3314

---------

Signed-off-by: Bernát Gábor <bgabor8@bloomberg.net>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>