Add PSScriptAnalyzer action

[SamErde]

Adds an action that runs PSScriptAnalyzer for any commits or pull requests against the testing branch.

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[TrimarcJake]

I have no idea how to test this without merging, so lfg.

[SamErde]

Cool. I've tested it in two branches of my fork--but it has actually been a good while since I've tested it with a failed lint check. Note, I specifically configured it for now to only run on the testing branch, but it may also run for branches based on testing.