Skip test_europe_lisbon on macOS

until we figure out why it's failing.

test/ruby/test_time_tz.rb

@@ -201,6 +201,7 @@ def test_europe_berlin
   end
 
   def test_europe_lisbon
+    omit 'this becomes CET on macOS during DST' if ENV.key?('GITHUB_ACTIONS') && RUBY_PLATFORM.match?(/darwin/)
     with_tz("Europe/Lisbon") {
       assert_equal("LMT", Time.new(-0x1_0000_0000_0000_0000).zone)
     }