test(mysql): provide concrete DBAPI connection attributes in mocks (#4116)

* test(mysql): provide concrete DBAPI connection attributes in mocks

* test(mysql): pass concrete attributes via MagicMock helpers

* test(mysql): refactor mocks and remove redundant attribute assignments

* changelog: add mysql test mock fix entry

* test(mysql): refactor SQL commenter mocks into helper

* test(mysql): refactor SQL commenter mocks into helper

- Introduce make_mysql_commenter_mocks helper
- Remove duplicated MagicMock setup
- Preserve test assertions and behavior
- Improve readability and maintainability

* test(mysql): use concrete DBAPI connection attributes in mocks to fix attribute type warnings

* Update instrumentation/opentelemetry-instrumentation-mysql/tests/test_mysql_integration.py

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Co-authored-by: Riccardo Magliocchetti <riccardo.magliocchetti@gmail.com>