[rubygems/rubygems] Use Regexp with refute_match

https://github.com/rubygems/rubygems/commit/51fdbe53bc

test/rubygems/test_gem_commands_help_command.rb

@@ -48,7 +48,7 @@ class TestGemCommandsHelpCommand < Gem::TestCase
       if Gem::HAVE_OPENSSL
         assert_empty err
 
-        refute_match 'No command found for ', out
+        refute_match %r|No command found for |, out
       end
     end
   end

test/rubygems/test_gem_specification.rb

@@ -2619,7 +2619,7 @@ end
   def test_to_yaml
     yaml_str = @a1.to_yaml
 
-    refute_match '!!null', yaml_str
+    refute_match %r|!!null|, yaml_str
 
     same_spec = Gem::Specification.from_yaml(yaml_str)
 

test/rubygems/test_remote_fetch_error.rb

@@ -4,7 +4,7 @@ require 'rubygems/test_case'
 class TestRemoteFetchError < Gem::TestCase
   def test_password_redacted
     error = Gem::RemoteFetcher::FetchError.new('There was an error fetching', 'https://user:secret@gemsource.org')
-    refute_match 'secret', error.to_s
+    refute_match %r|secret|, error.to_s
   end
 
   def test_invalid_url