Github actions: add ruby 3.2, remove rubies < 2.6

Author: Louis Lambeau

.github/workflows/integration.yml

@@ -13,7 +13,7 @@ jobs:
       fail-fast: false
       matrix:
         # Due to https://github.com/actions/runner/issues/849, we have to use quotes for '3.0'
-        ruby: [2.4, 2.5, 2.6, 2.7, 3.1]
+        ruby: [2.6, 2.7, 3.1, 3.2]
     env:
       SLACK_WEBHOOK_URL: ${{ secrets.SLACK_WEBHOOK_URL }}
     steps: