glprototypes: Add GST_GL_API_OPENGL to available version of sync

Make sync APIs usable if supported, even when GST_GL_API_OPENGL3 is
not selected

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-base/-/merge_requests/1215>

gst-libs/gst/gl/glprototypes/sync.h

@@ -19,7 +19,8 @@
  */
 
 GST_GL_EXT_BEGIN (sync,
-                  GST_GL_API_OPENGL3 | GST_GL_API_GLES2,
+                  GST_GL_API_OPENGL3 | GST_GL_API_OPENGL |
+                  GST_GL_API_GLES2,
                   3, 2,
                   3, 0,
                   "APPLE\0",