CI: read_clipboard / to_clipboard not working in Azure
The clipboard system does not work in Azure Pipelines. I tried the next things:

Installing `xsel` and `xclip` (separately) as suggested in the documentation

Setting up a step in the azure settings based on the travis docs:
```
  - script: |
      set -x
      sudo apt-get install -y xsel xvfb
      export DISPLAY=":99.0"
      sh -e /etc/init.d/xvfb start
      sleep 3
    displayName: 'Setup clipboard'
```

But we still get the same paperclyp error. This is affecting the docs (see #26852) and also the tests (see #26428).