[ruby/prism] Check void values in singleton class (`class <<`)

Follow up the ruby/ruby#8917 change.

https://github.com/ruby/prism/commit/f6bac4d3bf

prism/prism.c

@@ -14546,7 +14546,7 @@ parse_expression_prefix(pm_parser_t *parser, pm_binding_power_t binding_power) {
 
             if (accept1(parser, PM_TOKEN_LESS_LESS)) {
                 pm_token_t operator = parser->previous;
-                pm_node_t *expression = parse_expression(parser, PM_BINDING_POWER_NOT, PM_ERR_EXPECT_EXPRESSION_AFTER_LESS_LESS);
+                pm_node_t *expression = parse_value_expression(parser, PM_BINDING_POWER_NOT, PM_ERR_EXPECT_EXPRESSION_AFTER_LESS_LESS);
 
                 pm_parser_scope_push(parser, true);
                 accept2(parser, PM_TOKEN_NEWLINE, PM_TOKEN_SEMICOLON);

test/prism/errors_test.rb

@@ -1508,6 +1508,8 @@ module Prism
         end
         class A < (return)
         end
+        class << (return)
+        end
         for x in (return)
         end
       RUBY
@@ -1520,6 +1522,7 @@ module Prism
         [message, 80..86],
         [message, 110..116],
         [message, 132..138],
+        [message, 154..160],
       ], compare_ripper: false # Ripper does not check 'void value expression'.
     end