Missing files fin POTFILES.in
Damned lies reports the following issue:
There are some missing files from POTFILES.in:
- subprojects/gfm/gtkfilterlistmodel.c
- subprojects/gfm/gtkflattenlistmodel.c
- subprojects/gfm/gtkslicelistmodel.c
- subprojects/gfm/gtksortlistmodel.c