[Backport 1.2.latest] Pin `macos` runners to `macos-12` (#1016) #2640

Job	Run time
build packages	19s
code-quality	1m 48s
unit test / python 3.7	1m 41s
unit test / python 3.8	59s
unit test / python 3.9	1m 4s
unit test / python 3.10	1m 5s
verify packages / python 3.7 / ubuntu-latest	29s
verify packages / python 3.8 / ubuntu-latest	32s
verify packages / python 3.9 / ubuntu-latest	32s
verify packages / python 3.10 / ubuntu-latest	33s
verify packages / python 3.7 / macos-12	1m 11s
verify packages / python 3.8 / macos-12	1m 4s
verify packages / python 3.9 / macos-12	55s
verify packages / python 3.10 / macos-12	1m 5s
verify packages / python 3.7 / windows-latest	1m 46s
verify packages / python 3.8 / windows-latest	2m 4s
verify packages / python 3.9 / windows-latest	1m 45s
verify packages / python 3.10 / windows-latest	2m 19s
	21m 11s

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