We should only tier to Sparkplug from Ignition. Previously, the
'!ActiveTierIsSparkplug' condition was correct since only Ignition (and
Sparkplug itself) entered the TieringManager. But now that Maglev is
also present, the condition must be clarified to 'ActiveTierIsIgnition'.

Bug: v8:7700
Change-Id: Ic7ea898facf9ce65407d09cead35e0181e49db31
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3835562
Commit-Queue: Jakob Linke <jgruber@chromium.org>
Reviewed-by: Victor Gomes <victorgomes@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82519}