workflows: don't test paths on master.

[MikeMcQuaid]

This avoids weirdness like the merged PR commits being pushed to scheduled opened PRs after merging.

It also avoids wasting resources.

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• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same change?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes? Here's an example.
• Have you successfully run brew style with your changes locally?
• Have you successfully run brew tests with your changes locally?

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[dawidd6]

Maybe just:

branches-ignore:
  - master

would be sufficient?

[MikeMcQuaid]

@dawidd6 Thanks, pushed.