[ci] Move check-runtime-migration to GHA #7076

Job	Run time
set-image	8s
check-runtime-migration (westend)	6m 55s
check-runtime-migration (rococo)	4m 50s
check-runtime-migration (asset-hub-westend)	4m 18s
check-runtime-migration (asset-hub-rococo)	6m 3s
check-runtime-migration (bridge-hub-westend)	3m 53s
check-runtime-migration (bridge-hub-rococo)	3m 40s
check-runtime-migration (contracts-rococo)	3m 42s
check-runtime-migration (collectives-westend)	3m 43s
check-runtime-migration (coretime-rococo)	3m 45s
All runtime migrations passed	1s
	40m 58s

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