When --always-sparkplug, we compile on the main thread. This fixes the
CodeBuilder path when also running with --concurrent-sparkplug

Bug: v8:12054
Change-Id: Ifafcd68b635e99ca39c5eebc3e1ff839a2193eb4
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3233232
Commit-Queue: Victor Gomes <victorgomes@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Auto-Submit: Victor Gomes <victorgomes@chromium.org>
Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77470}