status/volume: Ignore capitalization for headphone detection

When we can't detect a headphone by form factor, we do a string
match on the port name. A match on 'Headphone' isn't less likely
to be valid than a match on 'headphone', so make sure we ignore
capitalization.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2691>

js/ui/status/volume.js

@@ -319,7 +319,7 @@ class OutputStreamSlider extends StreamSlider {
         // of different identifiers for headphones, and I could
         // not find the complete list
         if (sink.get_ports().length > 0)
-            return sink.get_port().port.includes('headphone');
+            return sink.get_port().port.toLowerCase().includes('headphone');
 
         return false;
     }