[Minor] Fix warning

src/client/rspamc.cxx

@@ -1034,8 +1034,8 @@ rspamc_symbols_output(FILE *out, ucl_object_t *obj)
 				fmt::print(out, "Message - {}: {}\n",
 						ucl_object_key(cmesg), ucl_object_tostring(cmesg));
 			} else {
-				unsigned char *rendered_message;
-				rendered_message = ucl_object_emit(cmesg, UCL_EMIT_JSON_COMPACT);
+				char *rendered_message;
+				rendered_message = (char *)ucl_object_emit(cmesg, UCL_EMIT_JSON_COMPACT);
 				fmt::print(out, "Message - {}: {:.60}\n",
 						ucl_object_key(cmesg), rendered_message);
 				free(rendered_message);