Pin the MCP conformance tester package #1721

Job	Run time
build (macos-latest, Debug)	10m 18s
build (macos-latest, Release)	7m 14s
build (ubuntu-latest, Debug)	12m 9s
build (windows-latest, Debug)	13m 40s
build (windows-latest, Release)	16m 44s
build (ubuntu-latest, Release)	11m 22s
publish-coverage	-1s
	1h 11m 26s

Provide feedback