Formats: Fix adding with context to bilingual PO file

Author: nijel

weblate/formats/ttkit.py

@@ -371,6 +371,8 @@ def create_unit(
                 target = multistring(target)
         if key:
             unit.setid(key)
+            if hasattr(unit, "setcontext"):
+                unit.setcontext(key)
         elif target is not None and self.set_context_bilingual:
             unit.setid(context)
             unit.context = context