Add a GitHub workflow for pull requests to Playground.
Add a GitHub workflow for pull requests to Playground.

Test: Needs testing with a GitHub runner.
Change-Id: I45f98759302de32824b044df8905308929e50ea6

AndroidX/androidx,androidx/androidx,AndroidX/androidx,AndroidX/androidx,androidx/androidx,androidx/androidx,AndroidX/androidx,androidx/androidx,androidx/androidx,androidx/androidx,AndroidX/androidx,AndroidX/androidx,androidx/androidx,AndroidX/androidx,AndroidX/androidx,AndroidX/androidx,androidx/androidx,AndroidX/androidx,androidx/androidx,androidx/androidx