[CT-1579] Split integration tests into groups

[MichelleArk]

We can use the pytest-split pytest plugin (or an alternative?) to split long-running integration test suites into groups and run the groups in parallel to speed up CI times.

Draft example for how this could look: #6346

Considerations

• Discovered some flaky tests that had dependencies on other tests for their success in the draft. We should aim to detect resolve as many of these as possible prior to introducing test groups else more flakiness may be discovered in unrelated PRs.
• More GHA tasks => more email clutter when things fail
• Integration test results are currently uploaded in a unified (all tests for python-version/os) form at the end of the workflow. How is this data used? Is it feasible to stitch together separate artifacts (one per python-version/os/group) into a unified view? using dbt??

[dbeatty10]

➕ Speeding up CI times would be awesome!

[github-actions]

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