GCs should reset memory pressure back to none on GC. Especially with
background threads calling MemoryPressureNotification to start a
collection.

Bug: v8:10315
Change-Id: I4dbda71e8434eb7949c0f9b978662b32910133cc
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2418400Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69996}