Ignore test_ractor.rb on non-Ractor ruby

Author: nobu

test/digest/test_ractor.rb

@@ -13,10 +13,6 @@ module TestDigestRactor
   Data1 = "abc"
   Data2 = "abcdbcdecdefdefgefghfghighijhijkijkljklmklmnlmnomnopnopq"
 
-  def setup
-    pend unless defined?(Ractor)
-  end
-
   def test_s_hexdigest
     assert_in_out_err([], <<-"end;", ["true", "true"], [])
       $VERBOSE = nil
@@ -98,4 +94,4 @@ class TestRMD160Ractor < Test::Unit::TestCase
       Data2 => "12a053384a9c0c88e405a06c27dcf49ada62eb2b",
     }
   end if defined?(Digest::RMD160)
-end
+end if defined?(Ractor)