Add Ruby 4.0 to CI

Author: jeremyevans

.github/workflows/ci.yml

@@ -11,7 +11,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [ ubuntu-latest ]
-        ruby: [ 2.0.0, 2.1, 2.3, 2.4, 2.5, 2.6, 2.7, '3.0', 3.1, 3.2, 3.3, 3.4, jruby-9.3, jruby-9.4, jruby-10.0 ]
+        ruby: [ 2.0.0, 2.1, 2.3, 2.4, 2.5, 2.6, 2.7, '3.0', 3.1, 3.2, 3.3, 3.4, "4.0", jruby-9.3, jruby-9.4, jruby-10.0 ]
         gemfile: [ Gemfile, Gemfile.rack-1.x ]
         exclude:
           - ruby: 2.0.0