workflows/docker: use GitHub Packages for caching. #31249

Job	Run time
syntax	45s
tap syntax	7m 29s
formula audit	4m 35s
cask audit	2m 24s
test default formula (Ubuntu 22.04)	1m 38s
test default formula (Ubuntu 20.04)	2m 47s
tests (online)	5m 6s
test default formula (macOS 13 x86_64)	3m 24s
update-test (Ubuntu)	24s
tests (generic OS)	3m 4s
vendored gems	42s
test default formula (macOS 15 arm64)	1m 17s
update-test (macOS)	28s
tests (Ubuntu 24.04)	2m 57s
tests (Ubuntu 22.04)	3m 0s
tests (Ubuntu 20.04)	3m 54s
tests (macOS 13 x86_64)	10m 40s
tests (macOS 15 arm64)	4m 26s
	59m 0s

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