CI against an older RuboCop version

1.69.2 was only just recently released.
Since 3.4 changed hash inspect formatting, some specs now fail.
Instead, bump the ruby version against rubocop master
which is equiped to handle these changes.
Now it again tests against a version that is about one year old

.github/workflows/rubocop.yml

@@ -104,8 +104,8 @@ jobs:
         rubocop: [master]
         internal_investigation: [null]
         include:
-          - { rubocop: master, ruby: "3.0", os: ubuntu }
-          - { rubocop: "v1.69.2", ruby: "3.4", os: ubuntu }
+          - { rubocop: master, ruby: "3.4", os: ubuntu }
+          - { rubocop: "v1.61.0", ruby: "2.7", os: ubuntu }
     steps:
       - name: checkout
         uses: actions/checkout@v4