Workaround for `Prism::ParseTest#test_filepath` for "unparser/corpus/literal/def.txt"

See the discussion on https://github.com/ruby/ruby/pull/9923

parse.y

@@ -9412,7 +9412,17 @@ formal_argument(struct parser_params *p, ID id)
 #undef ERR
     }
     shadowing_lvar(p, id);
+
+/*
+ * Workaround for Prism::ParseTest#test_filepath for "unparser/corpus/literal/def.txt"
+ *
+ * See the discussion on https://github.com/ruby/ruby/pull/9923
+ */
+#ifndef RIPPER
     return id;
+#else
+    return 0;
+#endif
 }
 
 #ifdef RIPPER

test/prism/parse_test.rb

@@ -207,8 +207,6 @@ module Prism
       # https://bugs.ruby-lang.org/issues/19539
       ripper_should_parse = false if relative == "heredocs_leading_whitespace.txt" && RUBY_VERSION < "3.3.0"
 
-      ripper_should_parse = false if relative == "unparser/corpus/literal/def.txt"
-
       define_method "test_filepath_#{relative}" do
         # First, read the source from the filepath. Use binmode to avoid converting CRLF on Windows,
         # and explicitly set the external encoding to UTF-8 to override the binmode default.