Have translatable strings for the torstatus GNOME Shell extension added to tails.pot (refs: #15715).

Previously, refresh-translations extracted them into tmp/pot/extension.js.pot
but then nothing more happened because that file was not in po/POTFILES.in.
So the strings (e.g. "Open Onion Circuits") did not end up in tails.pot, never
got translated, and were always displayed in English in the GUI.