AI: fix size of Opt in Dialog header

I think this got changed by accident during the Greenlines, as the
styles were not updated.

Bug: 477911897
Change-Id: I4cd5ae1c9ebc531fe09f5c9341defb622f3a2256
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/7761587
Auto-Submit: Jack Franklin <jacktfranklin@chromium.org>
Reviewed-by: Kateryna Prokopenko <kprokopenko@chromium.org>
Commit-Queue: Jack Franklin <jacktfranklin@chromium.org>

Author: jackfranklin

front_end/panels/ai_assistance/components/optInChangeDialog.css

@@ -25,7 +25,7 @@
     gap: var(--sys-size-8);
     margin-bottom: var(--sys-size-8);
 
-    h2 {
+    h1 {
       margin: 0;
       color: var(--sys-color-on-surface);
       font: var(--sys-typescale-headline5);