ci: ruby-saml's downstream test suite needs minitest compat

(cherry picked from commit 87d3c11)

.github/workflows/downstream.yml

@@ -47,7 +47,7 @@ jobs:
             command: "bundle exec rake spec"
           - url: https://github.com/SAML-Toolkits/ruby-saml
             name: ruby-saml
-            command: "bundle exec rake test"
+            command: "bundle exec rake test MT_COMPAT=t"
           # - url: https://github.com/instructure/nokogiri-xmlsec-instructure
           #   name: nokogiri-xmlsec-instructure
           #   precommand: "apt install -y libxmlsec1-dev"