UI/AppKit: Only check the NSEvent isARepeat flag in key down/up events

We call ns_event_to_key_event for the NSFlagsChanged event as well. By
retrieving the isARepeat flag on those events, we are guaranteed to
throw an exception.

See:
https://developer.apple.com/documentation/appkit/nsevent/1528049-arepeat?language=objc

    Raises an NSInternalInconsistencyException if sent to an
    NSFlagsChanged event or other non-key event.

Ladybird/AppKit/UI/Event.mm

@@ -297,7 +297,7 @@ explicit KeyData(NSEvent* event)
 {
     auto modifiers = ns_modifiers_to_key_modifiers(event.modifierFlags);
     auto key_code = ns_key_code_to_key_code(event.keyCode, modifiers);
-    auto repeat = event.isARepeat;
+    auto repeat = false;
 
     // FIXME: WebContent should really support multi-code point key events.
     u32 code_point = 0;
@@ -307,6 +307,8 @@ explicit KeyData(NSEvent* event)
         Utf8View utf8_view { StringView { utf8, strlen(utf8) } };
 
         code_point = utf8_view.is_empty() ? 0u : *utf8_view.begin();
+
+        repeat = event.isARepeat;
     }
 
     // NSEvent assigns PUA code points to to functional keys, e.g. arrow keys. Do not propagate them.