Add Rails 8.0.0 to CI matrix

Exclude AA 3.2.0 from Rails 8 as it predates Rails 8 support.

Author: Fivell

.github/workflows/test.yml

@@ -11,8 +11,11 @@ jobs:
       fail-fast: false
       matrix:
         ruby: ['3.2', '3.3', '3.4']
-        rails: ['7.1.0', '7.2.0']
+        rails: ['7.1.0', '7.2.0', '8.0.0']
         activeadmin: ['3.2.0', '3.3.0', '3.4.0', '3.5.1']
+        exclude:
+          - rails: '8.0.0'
+            activeadmin: '3.2.0'
     env:
       RAILS: ${{ matrix.rails }}
       AA: ${{ matrix.activeadmin }}