Build fails for PRs opened from forks

[alexvanyo]

snippets/.github/workflows/build.yml

Lines 31 to 34 in 87948ac

	steps:
	- uses: actions/checkout@v3
	with:
	token: ${{ secrets.PAT}}

The checkout build step uses a secret PAT, which forks don't have access to, so the build step immediately fails for any PRs opened from a fork.

Example PR: #178

[arriolac]

I made changes to fix the PAT-specific issue here. Builds are still failing though in the following workflow file: https://github.com/android/snippets/blob/main/.github/workflows/apply_spotless.yml. See: https://github.com/android/snippets/actions/runs/7806615803