[calls] po: Ignore subprojects

[Evangelos Ribeiro Tzaras <devrtz src gnome org>]

commit daebcf543aee8549d06c62c756f2744b15478070
Author: Evangelos Ribeiro Tzaras <devrtz fortysixandtwo eu>
Date:   Fri Oct 1 18:34:53 2021 +0200

    po: Ignore subprojects

 po/POTFILES.skip | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/po/POTFILES.skip b/po/POTFILES.skip
index 7ca29e61..e86c8026 100644
--- a/po/POTFILES.skip
+++ b/po/POTFILES.skip
@@ -6,3 +6,4 @@ plugins/mm/calls-mm-provider.c
 plugins/ofono/calls-ofono-call.c
 plugins/ofono/calls-ofono-origin.c
 plugins/ofono/calls-ofono-provider.c
+subprojects/**