assrender: Handle ".ttc" attachment extension

TTC stands for "TrueType Collection" file. We can pass it
into libass as any other attachment. Add it to the supported
extensions list, so the fonts it contains will be used.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/1481>

subprojects/gst-plugins-bad/ext/assrender/gstassrender.c

@@ -1558,7 +1558,8 @@ gst_ass_render_handle_tag_sample (GstAssRender * render, GstSample * sample)
   };
   static const gchar *extensions[] = {
     ".otf",
-    ".ttf"
+    ".ttf",
+    ".ttc"
   };
 
   GstBuffer *buf;