Add option to control max build concurrency #2659

Job	Run time
license header check	6s
mdBook Check	7s
typo-check	5s
CCAA-check	5s
stable-test (ubuntu-latest)	2m 49s
stable-test (macos-latest)	2m 34s
bleeding-test (ubuntu-latest)	2m 32s
stable-test (macos-13)	3m 54s
bleeding-test (macos-latest)	2m 0s
stable-test (windows-latest)	3m 39s
bleeding-test (macos-13)	6m 16s
bleeding-test (windows-latest)	3m 44s
coverage	0s
	27m 51s

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