Add run: option under test-on-pr.yml to allow running custom CLI commands like extra pip install.

[bobleesj]

What problem does this PR address?

Closes #164

run: commands works:

jobs:
  tests-on-pr:
    uses: bobleesj/release-scripts/.github/workflows/_tests-on-pr.yml@run-command
    with:
      project: bobleesj.release
      c_extension: false
      headless: false
      run: |
        pip install gooey
        echo "Done"

Ref CI: https://github.com/bobleesj-test-org/bobleesj.release/actions/runs/15895768623/job/44826878474?pr=31

What should the reviewer(s) do?

Please review and merge.

• This PR introduces a public-facing change (e.g., figures, CLI input/output, API).
  • Documentation (e.g., tutorials, examples, README) has been updated.
  • A tracking issue or plan to update documentation exists.
• This PR affects internal functionality only (no user-facing change).

[bobleesj]

@sbillinge This is ready to be merged. Once merged, we can then merge from main to v0.

[sbillinge]

@bobleesj sweet! can you let Zhi Ming know and he can test it for the gooey load....

[bobleesj]

yup sent a slack msg to zhiming to test