workflows/docker: use GitHub Packages for caching. #31252

Job	Run time
syntax	50s
tap syntax	7m 37s
formula audit	4m 42s
cask audit	2m 25s
tests (online)	5m 47s
update-test (Ubuntu)	23s
tests (generic OS)	2m 45s
vendored gems	1m 27s
update-test (macOS)	19s
tests (Ubuntu 24.04)	3m 9s
tests (Ubuntu 22.04)	3m 6s
test default formula (Ubuntu 22.04)	1m 35s
tests (Ubuntu 20.04)	4m 4s
test default formula (Ubuntu 20.04)	3m 45s
test default formula (macOS 13 x86_64)	3m 45s
tests (macOS 13 x86_64)	10m 59s
test default formula (macOS 15 arm64)	1m 18s
tests (macOS 15 arm64)	5m 18s
	1h 3m 14s

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