Move to composite run steps action

[helen]

Parallel to 10up/action-wordpress-plugin-deploy#74, where the Debian image is failing because of a new Debian release. This is almost certainly going to happen here as well, it's just used less often than the other action.

Alternate Designs

n/a

Benefits

Isn't broken, runs super fast

Possible Drawbacks

No drawbacks although it's not fixing any other reported bugs

Verification Process

Brought over the same changes from what worked in the other action, still haven't manually tested though.

Checklist:

• I have read the CONTRIBUTING document.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests passed.

Applicable Issues

I didn't open one, oops. See 10up/action-wordpress-plugin-deploy#73

Changelog Entry

Still needs