Fix masked license validation tests

[w3lld1]

Summary

I renamed the two colliding license rule files so each generated validation test receives a distinct Python name. I also added a regression test that rejects future rule-file name collisions, and updated the contributor and changelog entries.

Validation

I ran:

• PYTHONPATH=src pytest -q tests/licensedcode/test_rule_file_names.py
• ruff check tests/licensedcode/test_rule_file_names.py
• ruff format --check tests/licensedcode/test_rule_file_names.py
• python -m py_compile tests/licensedcode/test_rule_file_names.py
• git diff --check origin/develop...HEAD
• A tracked-file check across all 36,482 rule files confirming that no generated Python names collide

I did not run the full 29,000+ test suite locally; I deferred it to CI because the focused regression and static checks cover the changed path.

Tasks

• I reviewed the contribution guidelines
• I linked the original issue
• I used a uniquely named branch with one focused commit
• I added a regression test
• I updated CHANGELOG.rst
• I updated AUTHORS.rst

Fixes #5257

[w3lld1]

Fixed the license-data-sensitive CI failure in c0fa6d763 by updating the expected query spans after the rule-file renames changed the license index.

Fresh validation:

• venv/bin/pytest -q tests/licensedcode/test_detect.py::TestMatchAccuracyWithFullIndex::test_match_has_correct_line_positions_in_automake_perl_file
• venv/bin/pytest -q tests/licensedcode/test_rule_file_names.py
• git diff --check