Suppress a RuboCop offense

Follow up rubocop/rubocop#10715 and
suppresses the following offense:

```console
lib/rubocop/ast/node_pattern/compiler/binding.rb:24:31: C:
Layout/LineContinuationLeadingSpace: Move leading spaces to the end of
previous line.
                             " union and can't be used outside that union"
                              ^

162 files inspected, 1 offense detected
```

lib/rubocop/ast/node_pattern/compiler/binding.rb

@@ -20,8 +20,8 @@ def bind(name)
             end
 
             if var == :forbidden_unification
-              raise Invalid, "Wildcard #{name} was first seen in a subset of a" \
-                             " union and can't be used outside that union"
+              raise Invalid, "Wildcard #{name} was first seen in a subset of a " \
+                             "union and can't be used outside that union"
             end
             var
           end