Build: Harden GitHub Actions workflow permissions #314

Job	Run time
Build apps (Gplay, Debug, app)	4m 35s
Lint vitals (Foss, Beta, app)	3m 6s
Lint vitals (Gplay, Beta, app)	2m 52s
Unit tests (Debug, testFoss)	3m 28s
Build apps (Foss, Debug, app)	4m 36s
Lint vitals (Foss, Release, app)	3m 8s
Lint vitals (Gplay, Release, app)	3m 2s
Unit tests (Debug, testGplay)	3m 16s
	28m 3s

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