gzip: add tests for memoryview with itemsize > 1 byte

[dstndstn]

This PR adds tests to test_gzip.py that an array with items larger than one byte correctly round-trips through GzipFile and gzip.compress -> gzip.decompress.

Python 3.12 broke this; these tests are to try to make sure that doesn't happen again.

[python-cla-bot]

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[dstndstn]

My attempt at filing a bug against Python3.12 was closed with wontfix: #141201

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[dstndstn]

the macOS CI failure looks unrelated (ssl).