CI: switch arm64 runners to GHA #1338

Job	Run time
Build Documentation	21s
Build and Lint	2m 3s
Run tests on arm64	1m 13s
Run tests on previous stable Go	3m 11s
Run tests (mainline)	1m 10s
Run tests (stable)	1m 10s
Run tests (6.6)	59s
Run tests (6.1)	1m 1s
Run tests (5.15)	1m 50s
Run tests (5.10)	1m 39s
Run tests (5.4)	1m 3s
Run tests (4.19)	1m 9s
Run tests (4.14)	1m 3s
Run tests (4.9)	1m 19s
	19m 11s

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