chore: add trove classifier for license

[oefe]

Description

PyPI and various other tools don't report any license for pytest-recording.

Apparently, these tools rely on the trove classifier, not on the license setting in pyproject.toml or the LICENSE file in the project tree.

Add the trove classifier for consistency and compatibility with these tools.

Checklist

• Created tests which fail without the change (if possible)
• All tests passing
• Added a changelog entry
• Extended the README / documentation, if necessary

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (85c3ffa) 100.00% compared to head (1f6cce7) 89.19%.

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Additional details and impacted files

@@             Coverage Diff              @@
##            master     #133       +/-   ##
============================================
- Coverage   100.00%   89.19%   -10.81%     
============================================
  Files            8        8               
  Lines          287      287               
  Branches        54       39       -15     
============================================
- Hits           287      256       -31     
- Misses           0       30       +30     
- Partials         0        1        +1     

see 1 file with indirect coverage changes

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[Stranger6667]

thanks!