Flatpak: pin ges to 1.14.4

There was a new release of ges which requires 1.14.5 version of
other gstreamer modules. GStreamer 1.14.5 hasn't landed yet landed in
the Sdk so we pin the module till then.

flatpak/org.gnome.Fractal.json

@@ -89,7 +89,7 @@
                 {
                     "type" : "git",
                     "url" : "https://gitlab.freedesktop.org/gstreamer/gst-editing-services.git",
-                    "branch" : "1.14"
+                    "tag" : "1.14.4"
                 }
             ]
         },