Keep --gc-interval precise wrt to the # of allocations needed for a
GC.

Bug: v8:12615
Change-Id: I1ff45ef709013427b5f27643e3a6135dd0f4025d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3485676Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79256}