* master: (107 commits)
  bpo-22057: Clarify eval() documentation (pythonGH-8812)
  bpo-34318: Convert deprecation warnings to errors in assertRaises() etc. (pythonGH-8623)
  bpo-22602: Raise an exception in the UTF-7 decoder for ill-formed sequences starting with "+". (pythonGH-8741)
  bpo-34415: Updated logging.Formatter docstring. (pythonGH-8811)
  bpo-34432: doc Mention complex and decimal.Decimal on str.format not about locales (pythonGH-8808)
  bpo-34381: refer to 'Running & Writing Tests' in README.rst (pythonGH-8797)
  Improve error message when mock.assert_has_calls fails (pythonGH-8205)
  Warn not to set SIGPIPE to SIG_DFL (python#6773)
  bpo-34419: selectmodule.c does not compile on HP-UX due to bpo-31938 (pythonGH-8796)
  bpo-34418: Fix HTTPErrorProcessor documentation (pythonGH-8793)
  bpo-34391: Fix ftplib test for TLS 1.3 (pythonGH-8787)
  bpo-34217: Use lowercase for windows headers (pythonGH-8472)
  bpo-34395: Fix memory leaks caused by incautious usage of PyMem_Resize(). (pythonGH-8756)
  bpo-34405: Updated to OpenSSL 1.1.0i for Windows builds. (pythonGH-8775)
  bpo-34384: Fix os.readlink() on Windows (pythonGH-8740)
  closes bpo-34400: Fix undefined behavior in parsetok(). (pythonGH-4439)
  bpo-34399: 2048 bits RSA keys and DH params (python#8762)
  Make regular expressions in test_tasks.py raw strings. (pythonGH-8759)
  smtplib documentation fixes (pythonGH-8708)
  Fix misindented yaml in logging how to example (pythonGH-8604)
  ...

824: Use context manager for assertWarns and fix DeprecationWarning r=hgrecco a=tirkarthi

* Fix `DeprecationWarning` to use collections.abc
* Starting from Python 3.8 `assertRaises` no longer accepts a None with python/cpython#8623 . So use a context manager and assert for `RuntimeWarning`

This fix unblock fedora to package the library for Python 3.8 : https://bugzilla.redhat.com/show_bug.cgi?id=1706212

Thanks

Co-authored-by: xtreak <tir.karthi@gmail.com>