Fix use of numbered parameter inside proc that is default value of optarg

This allows cases such as:

```ruby
m ->(a = ->{@1}) {a}
m.call.call(1)

m2 ->(a: ->{@1}) {a}
m2.call.call(2)
```

Previously, this would cause a syntax error.

[Bug#15789]

parse.y

@@ -3372,6 +3372,7 @@ lambda		:   {
 		    }
 		    {
 			$<num>$ = p->max_numparam;
+			p->max_numparam = 0;
 		    }
 		  f_larglist
 		    {