[GTK4] Bump minimum requirement to 4.6

https://bugs.webkit.org/show_bug.cgi?id=266220

Reviewed by Michael Catanzaro.

Although OptionsGTK.cmake advertises a minimum requirement of GTK 4.4,
Source/WebKit/UIProcess/API/gtk/WebKitWebViewBase.cpp makes use the
GDK_TOUCHPAD_HOLD enumeration symbol, which was not introduced until GTK
4.6.

Canonical link: https://commits.webkit.org/271889@main

Source/cmake/OptionsGTK.cmake

@@ -152,7 +152,7 @@ include(GStreamerDependencies)
 WEBKIT_OPTION_END()
 
 if (USE_GTK4)
-    set(GTK_MINIMUM_VERSION 4.4.0)
+    set(GTK_MINIMUM_VERSION 4.6.0)
     set(GTK_PC_NAME gtk4)
 else ()
     set(GTK_MINIMUM_VERSION 3.22.0)