Co-authored-by: kclark <kclark@autoverify.net>

ref #894

ref 430b12e#r62580685

* Do not require cloudpickle for PyPy

The cloudpickle package relies on CPython implementation details,
and does not even import on PyPy:

```
ImportError while importing test module '/tmp/attrs/tests/test_3rd_party.py'.
Hint: make sure your test modules/packages have valid Python names.
Traceback:
/usr/lib/pypy3.8/importlib/__init__.py:127: in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
tests/test_3rd_party.py:7: in <module>
    import cloudpickle
.tox/pypy3/lib/pypy3.8/site-packages/cloudpickle/__init__.py:4: in <module>
    from cloudpickle.cloudpickle import *  # noqa
.tox/pypy3/lib/pypy3.8/site-packages/cloudpickle/cloudpickle.py:57: in <module>
    from .compat import pickle
.tox/pypy3/lib/pypy3.8/site-packages/cloudpickle/compat.py:13: in <module>
    from _pickle import Pickler  # noqa: F401
E   ModuleNotFoundError: No module named '_pickle'
```

Disable the dependency for PyPy and make the test handle missing
cloudpickle gracefully.

* Enable testing on pypy-3.8

* add a news entry

Co-authored-by: Hynek Schlawack <hs@ox.cx>

* Make virtual repr file names unique

* Add newsfragments