Run comment only if coverage-combine completed

[yorickdowne]

Changes

Avoid failing comment action when we're not running the full test suite

Types of changes

What types of changes does your code introduce?

• Build-related changes

Testing

Requires testing

• Yes
• No

[yorickdowne]

This workflow runs from main. The only way to test it is to merge it, as far as I can tell.

[yorickdowne]

No it won't work that way. We really can't check on individual job status in a previous run without triggering a fail (see https://stackoverflow.com/questions/71963637/reusing-github-actions-jobs-results-from-a-workflow-when-called-on-workflow-run), so we'll always have a fail when we don't run tests.

C'est la vie. We can remove the conditional test running once we no longer pay for runners, if we like.