fix: src\class.c(949): warning C4244: '=': conversion from 'mrb_int' to 'int', possible loss of data

src/class.c

@@ -567,7 +567,7 @@ mrb_get_args(mrb_state *mrb, const char *format, ...)
 {
   const char *fmt = format;
   char c;
-  int i = 0;
+  mrb_int i = 0;
   va_list ap;
   mrb_int argc = mrb->c->ci->argc;
   int arg_i = 0;