Pin the MCP conformance tester package #1722

Job	Run time
build (windows-latest, Release)	9m 5s
build (ubuntu-latest, Release)	5m 54s
build (macos-latest, Release)	8m 10s
build (macos-latest, Debug)	7m 9s
build (windows-latest, Debug)	10m 5s
build (ubuntu-latest, Debug)	11m 3s
publish-coverage	0s
	51m 26s

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