Merge pull request #869 from varvet/kbs/ruby-4.0

Add Ruby 4.0 to matrix

Author: Burgestrand

.github/workflows/main.yml

@@ -28,6 +28,7 @@ jobs:
           - "3.2"
           - "3.3"
           - "3.4"
+          - "4.0"
           - "jruby-9.3.15"
           - "jruby"
         include: # HEAD-versions