Add Ruby 4.0 to CI

Author: jeremyevans

.github/workflows/ci.yml

@@ -16,7 +16,7 @@ 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-9.4, 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-9.4, jruby-10.0 ]
         include:
           - { os: ubuntu-22.04, ruby: jruby-9.2 }
     runs-on: ${{ matrix.os }}