update github actions to test rails 8

.github/workflows/main.yml

@@ -80,3 +80,19 @@ jobs:
         bundler-cache: true
     - name: Run tests
       run: bundle exec rake
+  test_rails_8:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        gemfile: [ 'Gemfile.rails-8.0' ]
+    env: # $BUNDLE_GEMFILE must be set at the job level, so it is set for all steps
+      BUNDLE_GEMFILE: ${{ github.workspace }}/${{ matrix.gemfile }}
+    steps:
+      - uses: actions/checkout@v4
+      - name: Set up Ruby
+        uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: 3.2
+          bundler-cache: true
+      - name: Run tests
+        run: bundle exec rake