RUST-DB: Use 2 characters codes even for added languages in the iso_639_1 table

src/rust/liblektor-rs/migrations/2022-09-30-204512_initial/up.sql

@@ -97,5 +97,5 @@ INSERT OR REPLACE INTO iso_639_1 (is_macro, is_iso, code, name_en) VALUES
   ( false, true, "zu", "Zulu"           ),
   -- The things we added because they were not defined in the ISO 639-1 and
   -- because we need them to distinguish some karas.
-  ( true,  false, "fiction", "Fictional" ),
-  ( true,  false, "autre",   "Joker"     );
+  ( true,  false, "fx", "Fictional"     ),
+  ( true,  false, "ot", "Joker"         );