ci: Normalize Windows sha256sum output for actions/attest #3070

Job	Run time
contract-tests-curl	3m 23s
build-test-client-mac-curl	4m 28s
contract-tests	3m 11s
build-test	5m 56s
build-test-client-windows-curl	14m 31s
build-test-client-windows	14m 29s
build-test-client-mac	3m 38s
build-test-curl	5m 54s
	55m 30s

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