Disable gc for now #491

Job	Run time
rust_ci (macos-latest, stable)	31s
rust_ci (macos-latest, beta)	41s
rust_ci (macos-latest, nightly)	30s
rust_ci (ubuntu-latest, stable)	24s
rust_ci (ubuntu-latest, beta)	39s
rust_ci (ubuntu-latest, nightly)	40s
rust_ci (windows-latest, stable)	25s
rust_ci (windows-latest, beta)	25s
rust_ci (windows-latest, nightly)	25s
	4m 40s

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