ci: Fix Test workflow concurrency for code coverage

[anomiex]

Proposed changes:

A few adjustments are needed to make the coverage stuff more reliable:

1. For trunk runs, don't cancel for concurrency. We need each trunk commit to upload.
2. If the actual run is cancelled, don't upload partial data.

Other information:

• Have you written new tests for your changes, if applicable?
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Does this pull request change what data or activity we track or use?

Testing instructions:

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[tbradsha]

Should we even try to run process-coverage if run-tests is cancelled? 🤔 Though I guess if it runs that's an easy way to determine if coverage was enabled and I'm not sure if matrix.script == 'test-coverage' is accessible here.

[anomiex]

For manual analysis, it probably doesn't hurt to save whatever coverage data we did manage to generate. But, particularly for trunk runs, it'll throw things off if that partial data gets uploaded.

The check here is now threefold: (1) we finished running the actual tests, (2) we successfully processed the coverage data, and (3) we successfully uploaded the artifact. If 2 or 3 is false, the upload job won't even be able to run successfully because there will be no data. If 1 is false, it's partial data that we don't want to upload.

[tbradsha]

Seems reasonable.