[PRISM] Disallow &. in MLHS

test/.excludes-prism/TestSyntax.rb

@@ -17,7 +17,6 @@ exclude(:test_keyword_self_reference, "unknown")
 exclude(:test_methoddef_endless_command, "unknown")
 exclude(:test_numbered_parameter, "unknown")
 exclude(:test_optional_self_reference, "unknown")
-exclude(:test_safe_call_in_massign_lhs, "unknown")
 exclude(:test_syntax_error_at_newline, "unknown")
 exclude(:test_unexpected_fraction, "unknown")
 exclude(:test_unterminated_heredoc_cr, "unknown")