CI: switch arm64 runners to GHA #1340

Job	Run time
Build Documentation	21s
Build and Lint	2m 5s
Run tests on previous stable Go	1m 39s
Run tests (mainline)	1m 10s
Run tests on arm64	20s
Run tests (stable)	1m 3s
Run tests (6.6)	1m 1s
Run tests (6.1)	1m 10s
Run tests (5.15)	1m 6s
Run tests (5.10)	1m 21s
Run tests (5.4)	1m 11s
Run tests (4.19)	1m 22s
Run tests (4.14)	1m 24s
Run tests (4.9)	1m 2s
	16m 15s

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