Fix strict options from addopts

[praneethhere]

Closes #14442

This fixes a pytest 9 regression where --strict-markers and
--strict-config were ignored when configured through addopts

addopts is parsed after the initial config discovery step, so the
OverrideIniAction compatibility path updated the parsed argparse namespace,
but the generated ini overrides were not applied back into _inicfg

As a result, later getini() calls still saw the default values for
strict_markers and strict_config

This change applies parsed ini overrides after parsing the full argument list
including addopts, and clears the ini cache so later getini() calls use the
updated values

Added regression coverage for:

• --strict-config from addopts
• --strict-markers from addopts

Tested with:

python -m pytest -q \
  testing/test_config.py::TestParseIni::test_strict_config_from_addopts \
  testing/test_mark.py::test_strict_markers_from_addopts

python -m pytest -q \
  testing/test_config.py::TestParseIni::test_invalid_config_options \
  testing/test_mark.py::test_strict_prohibits_unregistered_markers

[The-Compiler]

Thanks! I can't comment much about the approach you took here (I'd like to defer that to e.g. @bluetech), but I added two suggestions.

[The-Compiler]

Why run this a second time here? I don't see how pytest_addoption could somehow influence addopts.

If this is needed, can you please add a test to demonstrate that?

[The-Compiler]

I'd suggest matching on the actual return value, like in the other test you added.

[praneethhere]

@The-Compiler Thanks for the review

I originally added the second _inicfg update as a defensive follow up after the later argument parse, in case any parsed overrides changed at that point. After looking at this again, it is not needed for this regression. The important path is the first parse after addopts has been included, before the strict config and marker handling reads from getini()

I removed the second update to keep the change scoped to the failing case

Also updated marker regression test to assert the exact exit code