We only complete sweeping when the young generation GC is enabled.

Change-Id: I915acce35d6ba16716c2c4ee4130f99af0744f83
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3900377Reviewed-by: Anton Bikineev <bikineev@chromium.org>
Commit-Queue: Anton Bikineev <bikineev@chromium.org>
Auto-Submit: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#83269}