chore: pin third-party GitHub Actions to commit SHAs #1718

Job	Run time
build-test-server-mac	5m 22s
build-test-server-curl	7m 22s
contract-tests	4m 31s
build-test-server-windows	17m 22s
build-test-server-windows-curl	18m 20s
build-test-server-mac-curl	5m 26s
contract-tests-curl	4m 16s
build-test-server	7m 18s
	1h 9m 57s

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