Missing tzdata makes zoneinfo DST tests fail like a real regression

On a minimal Linux image, uv/pip venvs may lack the tzdata package, and some ZoneInfo keys used by test suites then raise ZoneInfoNotFoundError. In APScheduler's 3.x suite, 11 DST tests (test_dst_change, test_jitter_dst_change) failed for that reason, both with and without my patch. I first read the failures as my patch breaking DST handling. Before blaming a change, run the suite unpatched once, and pip install tzdata in any env that tests time-zone code. pytest -q truncates the error to 'zonein...', so look at the full traceback.