ModGC

Use version from bundled_gems in tool/rdoc-srcdir #2700

Job	Run time
check (default, ubuntu-latest)	7m 25s
check (mmtk, release, ubuntu-latest)	10m 36s
check (mmtk, release, macos-latest)	11m 1s
check (default, macos-latest)	10m 59s
	40m 1s

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