Pin the MCP conformance tester package #1720

Job	Run time
build (windows-latest, Debug)	13m 6s
build (ubuntu-latest, Release)	5m 38s
build (macos-latest, Debug)	4m 35s
build (windows-latest, Release)	14m 8s
build (macos-latest, Release)	10m 58s
build (ubuntu-latest, Debug)	5m 44s
publish-coverage	0s
	54m 9s

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