fix: missing localisation for topic move error

public/language/en-GB/error.json

@@ -193,6 +193,7 @@
 
 	"no-topics-selected": "No topics selected!",
 	"cant-move-to-same-topic": "Can't move post to same topic!",
+	"cant-move-topic-to-same-category": "Can't move topic to the same category!",
 
 	"cannot-block-self": "You cannot block yourself!",
 	"cannot-block-privileged": "You cannot block administrators or global moderators",