[ox/claw] Fix writeClawHeader to move return value

(synced from af7dbd1aee)

src/ox/claw/write.hpp

@@ -77,7 +77,7 @@ Result<String> writeClawHeader(T *t, ClawFormat fmt) noexcept {
 		out += tn;
 	}
 	out += ";";
-	return out;
+	return move(out);
 }
 
 }