Accept WTFPL as a GPL-compatible license

[davidperezgar]

Adds WTFPL (Do What The F*ck You Want To Public License) as a recognized GPL-compatible license in Plugin Check. The GNU license list marks WTFPL as GPL-compatible, but Plugin Check was flagging it as invalid.

Fixes #1157

Changes

• Updated is_license_gpl_compatible() in includes/Traits/License_Utils.php:
  • Added WTFPL to the regex pattern for GPL-compatible licenses
• Updated get_normalized_license() in includes/Traits/License_Utils.php:
  • Added normalization to convert WTFPL variations (e.g., "Do What The F*ck You Want To Public License") to "WTFPL"
• Added test cases in tests/phpunit/tests/Traits/License_Utils_Tests.php:
  • Normalization tests for WTFPL variations
  • GPL compatibility tests for WTFPL
• Added integration test in tests/phpunit/tests/Checker/Checks/Plugin_Header_Fields_Check_Tests.php:
  • test_run_with_valid_wtfpl_license() to verify WTFPL is accepted in plugin headers
• Created test plugin test-plugin-wtfpl-license with WTFPL license for integration testing

Benefits

• WTFPL is now recognized as GPL-compatible, aligning with the GNU license list
• Reduces false positives for valid GPL-compatible licenses
• Supports common WTFPL variations in plugin headers
• Maintains existing validation for other licenses

Checklist

• Code follows WordPress Coding Standards
• Self-reviewed the code
• Added necessary comments
• No new linter errors
• Added test cases to prevent regression
• All existing tests pass
• New tests pass
• Integration test created and verified

[github-actions]

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Co-authored-by: davidperezgar <davidperez@git.wordpress.org>
Co-authored-by: ernilambar <nilambar@git.wordpress.org>
Co-authored-by: frantorres <frantorres@git.wordpress.org>
Co-authored-by: nilovelez <nilovelez@git.wordpress.org>

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