doc: only apply content-visibility on all.html

Refs: #40099
PR-URL: #53510
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Moshe Atlow <moshe@atlow.co.il>
Reviewed-By: Claudio Wunder <cwunder@gnome.org>

doc/api_assets/style.css

@@ -434,7 +434,7 @@ dd + dt.pre {
   padding-top: 1rem;
 }
 
-#apicontent section {
+#api-section-all #apicontent section {
   content-visibility: auto;
   contain-intrinsic-size: 1px auto 5000px;
 }