[libadwaita] Update POTFILES.skip

[Piotr Drąg <piotrdrag src gnome org>]

commit 363b0abca638bec85d2caed70250a2307dc5ed06
Author: Piotr Drąg <piotrdrag gmail com>
Date:   Sat Dec 18 13:34:27 2021 +0100

    Update POTFILES.skip

 po/POTFILES.skip | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/po/POTFILES.skip b/po/POTFILES.skip
index 2a262dc7..c60b8aed 100644
--- a/po/POTFILES.skip
+++ b/po/POTFILES.skip
@@ -1,3 +1,4 @@
 # List of source files that should *not* be translated.
 # Please keep this file sorted alphabetically.
 demo/
+doc/