refactor: remove unused PYTEST_VERSION and packaging import

`PYTEST_VERSION` was computed but never referenced in the plugin;
pytest version differences are handled by duck-typing on
`report.longrepr` instead. Removing it also drops the runtime import
of `packaging`, which is not a declared dependency (it was only
available transitively via pytest).

Assisted-by: ClaudeCode:claude-opus-4.8

Author: henryiii

pytest_github_actions_annotate_failures/plugin.py

@@ -6,7 +6,6 @@
 
 import pytest
 from _pytest._code.code import ExceptionRepr, ReprEntry
-from packaging import version
 
 if TYPE_CHECKING:
     from warnings import WarningMessage
@@ -23,9 +22,6 @@
 # https://github.com/pytest-dev/pytest/blob/master/src/_pytest/terminal.py
 
 
-PYTEST_VERSION = version.parse(pytest.__version__)
-
-
 class _AnnotateErrors:
     @pytest.hookimpl(tryfirst=True)
     def pytest_runtest_logreport(self, report: TestReport):