Add Ruby 4.0 to matrix (#193)

Author: teoljungberg

.github/workflows/ci.yml

@@ -10,12 +10,11 @@ jobs:
   tests:
     name: Ruby ${{ matrix.ruby }}, Rails ${{ matrix.rails }}
     runs-on: ubuntu-latest
-    continue-on-error: ${{ matrix.ruby == 'head' }}
 
     strategy:
       fail-fast: false
       matrix:
-        ruby: ["3.2", "3.3", "3.4", "head"]
+        ruby: ["3.2", "3.3", "3.4", "4.0"]
         rails: ["7.2", "8.0", "8.1"]
 
     services: