Codechange: Suppress warnings when asserts are disabled (#8917)

src/tunnelbridge_cmd.cpp

@@ -1847,6 +1847,7 @@ static void ChangeTileOwner_TunnelBridge(TileIndex tile, Owner old_owner, Owner
 			/* Since all of our vehicles have been removed, it is safe to remove the rail
 			 * bridge / tunnel. */
 			CommandCost ret = DoCommand(tile, 0, 0, DC_EXEC | DC_BANKRUPT, CMD_LANDSCAPE_CLEAR);
+			(void)ret; // assert only
 			assert(ret.Succeeded());
 		} else {
 			/* In any other case, we can safely reassign the ownership to OWNER_NONE. */