Use GitHub-hosted macos-12 in CI, not deprecated macos-11 #22799

Job	Run time
Ensure PR has a category label	2s
Classify changes	3s
Bootstrap Pants, test Rust (Linux-ARM64)	2m 6s
Bootstrap Pants, test and lint Rust (Linux-x86_64)	8m 36s
Bootstrap Pants, test Rust (macOS12-x86_64)	11m 53s
Build wheels (Linux-ARM64)	0s
Ensure PR has release notes	2s
Build wheels (Linux-x86_64)	0s
Build wheels (macOS10-15-x86_64)	0s
Build wheels (macOS11-ARM64)	0s
Test Python (Linux-ARM64)	2m 20s
Test Python (Linux-x86_64) Shard 0/10	16m 3s
Test Python (Linux-x86_64) Shard 1/10	15m 49s
Lint Python and Shell	3m 11s
Test Python (Linux-x86_64) Shard 2/10	16m 2s
Test Python (Linux-x86_64) Shard 3/10	15m 22s
Test Python (Linux-x86_64) Shard 4/10	25m 53s
Test Python (Linux-x86_64) Shard 5/10	11m 59s
Test Python (Linux-x86_64) Shard 6/10	9m 52s
Test Python (Linux-x86_64) Shard 8/10	13m 41s
Test Python (Linux-x86_64) Shard 7/10	14m 46s
Test Python (Linux-x86_64) Shard 9/10	9m 25s
Test Python (macOS12-x86_64)	8m 8s
Set Merge OK	1s
Merge OK	1s
	3h 5m 15s

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