Also fix a couple other ignored PCbuild directories in .gitignore

Patch by Abhilash Raj.

Patch by Milan Oberkirch.

Made test_pprint discoverable.

Made test_pprint discoverable.

When not using decode_data=True, smtpd may provide keyword arguments to the
process_message user-implemented method.  This doc update is intended to make
it clear that arbitrary keywords must be supported, so that we can add
additional features in the future by just adding keywords to the
process_message call.

Initial patch by Milan Oberkirch.

assertWarnsRegex() checks now emits a deprecation warning when callable is
None or keyword arguments except msg is passed in the context manager mode.

Issue 24200.