Fix nil size Enumerator test

If the `size` is `nil`, which means the size is unknown:

1. Test with loop but break after 10,000 loops.
2. If the object has more than 10,000 objects, assume it’s an infinite loop.

This is clearly broken for enumerators with more than 10,000 but fixed size. But it works for tests.

Author: soutaro

lib/rbs/test/type_check.rb

@@ -288,6 +288,19 @@ def value(val, type)
                   values << args
                   nil
                 end
+              when nil
+                values = []
+                count = 10_000
+
+                ret = val.each do |*args|
+                  count -= 1
+                  values << args
+                  break if count <= 0
+                end
+
+                if count == 0
+                  ret = self
+                end
               else
                 values = []
                 ret = val.each do |*args|