[PRISM] Enable integer test

test/.excludes-prism/TestRubyLiteral.rb

@@ -2,5 +2,4 @@ exclude(:test_debug_frozen_string_in_array_literal, "unknown")
 exclude(:test_debug_frozen_string, "unknown")
 exclude(:test_dregexp, "https://github.com/ruby/prism/issues/2664")
 exclude(:test_hash_value_omission, "unknown")
-exclude(:test_integer, "unknown")
 exclude(:test_string, "https://github.com/ruby/prism/issues/2331")