test: upgrade min pytest to 9 and use native toml configuration

[Lee-W]

Description

Upgrade the min pytest version to 9 so that we can use native toml configuration (use [tool.pytest] instead of [tool.pytest.ini_options])

Checklist

• I have read the contributing guidelines

Code Changes

• [ ] Add test cases to all the changes you introduce
• Run uv run poe all locally to ensure this change passes linter check and tests
• Manually test the changes:
  • Verify the feature/bug fix works as expected in real-world scenarios
  • Test edge cases and error conditions
  • [ ] Ensure backward compatibility is maintained
  • [ ] Document any manual testing steps performed
• [ ] Update the documentation for the changes

Documentation Changes

• [ ] Run uv run poe doc locally to ensure the documentation pages renders correctly
• [ ] Check and fix any broken links (internal or external) in the documentation

When running uv run poe doc, any broken internal documentation links will be reported in the console output like this:

INFO    -  Doc file 'config.md' contains a link 'commands/bump.md#-post_bump_hooks', but the doc 'commands/bump.md' does not contain an anchor '#-post_bump_hooks'.

Expected Behavior

uv run poe test runs fine

Steps to Test This Pull Request

1. uv run poe test

Additional Context

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.88%. Comparing base (7327ae1) to head (462dc82).
⚠️ Report is 2 commits behind head on master.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1769   +/-   ##
=======================================
  Coverage   97.88%   97.88%           
=======================================
  Files          60       60           
  Lines        2606     2606           
=======================================
  Hits         2551     2551           
  Misses         55       55           

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