fix: src\error.c(76): warning C4244: '=': conversion from 'mrb_int' to 'int', possible loss of data

src/error.c

@@ -71,7 +71,7 @@ exc_exception(mrb_state *mrb, mrb_value self)
 {
   mrb_value exc;
   mrb_value a;
-  int argc;
+  mrb_int argc;
 
   argc = mrb_get_args(mrb, "|o", &a);
   if (argc == 0) return self;