TST: Avoid time dependency in GCS zip test
- [x] tests added / passed
- [x] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit) for how to run them

To avoid CI flakiness from this test, only compare the checksum of the ZIP contents to avoid comparing the flaky last modified timestamp of the ZIP archive. IMO, the CI stability is worth the the trade off of being a little less strict here.

cc @jbrockmendel 

this is fantastic LGTM