chore: pin third-party GitHub Actions to commit SHAs #2704

Job	Run time
build-test-client-mac-curl	4m 4s
contract-tests-curl	3m 23s
build-test-client-mac	4m 44s
build-test	6m 29s
build-test-curl	5m 50s
build-test-client-windows-curl	15m 5s
contract-tests	3m 17s
build-test-client-windows	13m 26s
	56m 18s

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