It is possible for IncrementalMarkingJob to be scheduled while MajorMC
is running, but it only gets to run after MajorMC finished.

If concurrent MinorMC is run in the meantime, RunInternal should not
invoke Step, which is currently only supported for MajorMC. This CL adds
a bailout for this case.

Bug: v8:13012
Change-Id: I3012cac3de5195a9f1b85f1ac18b02cef67b004b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3867516
Commit-Queue: Leon Bettscheider <bettscheider@google.com>
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82903}