Ensure `DisposeAsync` and `Dispose` are idempotent #2125

Job	Run time
call-build-test / build-win32	2m 45s
call-build-test / build-ubuntu	1m 11s
call-build-test / sequential-integration-ubuntu	9m 19s
call-build-test / integration-ubuntu	4m 12s
call-build-test / sequential-integration-win32	21m 24s
call-build-test / integration-win32	11m 41s
	50m 32s

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