[iOS] Fix font issue in the PromoStyleViewController

This patch should be cherry-picked in M124.
Bug introduced with crrev.com/c/5386141.

MiniMapInterstitialViewController and NotificationsOptInViewController
are subclasses of PromoStyleViewController and they both override
-[PromoStyleViewController titleLabelFontTextStyle].

This patch make sure the value for -[self titleLabelFontTextStyle] is
used to generate the title font.

Fixed: 331398281
Change-Id: I6f59cfbe67436358154a406b1679d7810bee52b9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5398496


Auto-Submit: Jérôme Lebel <jlebel@chromium.org>
Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Commit-Queue: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1278840}