"<ex_n>" "<prop>" -> "<ex_np>"

Fixes https://giellatekno.uit.no/bugzilla/show_bug.cgi?id=2701

tools/mt/apertium/tagsets/modify-tags.regex

@@ -2,6 +2,7 @@
   [ "<n>" "<prop>" "<sem_plc>" -> "<np>" "<top>" ] .o.
   [ "<n>" "<prop>" "<sem_org>" -> "<np>" "<org>" ] .o.
   [ "<n>" "<prop>" -> "<np>" ] .o.
+  [ "<ex_n>" "<prop>" -> "<ex_np>" ] .o.
   [ "<g3>" "<n>"   -> "<n>" "<g3>" ] .o.
   [ "<g7>"    -> 0  ] .o.
   [ "<gram_3syll>"    -> 0  ] .o.