Add Ruby 4.0 to CI

Author: jeremyevans

.github/workflows/ci.yml

@@ -15,7 +15,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        ruby: [ 3.2, 3.3, 3.4, jruby-9.4, jruby-10.0 ]
+        ruby: [ 3.2, 3.3, 3.4, "4.0", jruby-9.4, jruby-10.0 ]
     name: ${{ matrix.ruby }}
     env:
       BUNDLE_GEMFILE: .ci.gemfile