CI: Test rack-protection with Ruby 4.0 (sinatra#2137)

Author: dentarg

.github/workflows/test.yml

@@ -26,6 +26,7 @@ jobs:
           - "3.2"
           - "3.3"
           - "3.4"
+          - "4.0"
           - "jruby"
           - "truffleruby"
         include: