Doc action can fail.

[rasolca]

I noticed that the doc action on master can fail if a PR is merged while the action is running.

It should not be a big problem as a new PR merge will trigger again the action that build the latest documentation.

However I'm not sure if it can impact a release doc generation if a PR is merge right before a release is tagged.

[rasolca]

https://github.com/eth-cscs/DLA-Future/actions/runs/9093013625/job/24991020675

To https://github.com/eth-cscs/DLA-Future
 ! [remote rejected] docs -> docs (cannot lock ref 'refs/heads/docs': is at fca3108d7808aba74109b41764496a988b8965bd but expected e535e2e424c8869d3dd26c6bc7d3c7319fe05d53)
error: failed to push some refs to 'https://github.com/eth-cscs/DLA-Future'```

[msimberg]

Maybe a use case for concurrency groups: https://docs.github.com/en/actions/using-jobs/using-concurrency#example-concurrency-groups?