Removing coverage cruft from test CI

[john-science]

What is the change?

I removed some old coverage stuff from the unit test CI.

Why is the change being made?

This is a remnant from back when the "coverage" and "unit test" CI were the same GitHub Workflows. There was an awful lot of back and forth to move CI features around over the preceding months. And since this extra stuff doesn't hurt anything it was missed.

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Checklist

• [x] This PR has only one purpose or idea.
• [x] Tests have been added/updated to verify any new/changed code.

• [x] The code style follows good practices.
• [x] The commit message(s) follow good practices.

• [x] The release notes have been updated if necessary.
• [x] The documentation is still up-to-date in the doc folder.
• [x] The dependencies are still up-to-date in pyproject.toml.