chore: adjust delete PR workflow name and set required permissions

[gwarf]

I think the deletion of PR preview never works, let's see if we can get it working.

[github-actions]

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[enolfc]

LGTM, but I guess we need to test again by merging

[gwarf]

@enolfc it seems to have worked at least when removing the label, I've tried removing it on #664:

• https://github.com/EGI-Federation/documentation/actions/runs/12688246198/job/35364361677 (there is apparently an old/obsolete/useless branch paramter, will make a PR to clean it)
• 33137ae

[gwarf]

Hm, there may still be issues, apparently it worked when adding/removing the label but not when merging the PR:

• Success when removing a label (AFAIU): https://github.com/EGI-Federation/documentation/actions/runs/12688246198/job/35364361677
• Error when merging (AFAIU): https://github.com/EGI-Federation/documentation/actions/runs/12688986914/job/35366700297

While the workflow file is apparently the same for both run, the permissions logged in the jobs are different:

vs

[gwarf]

Another different is that the working was for the PR #664, made in a feature branch in this repo while the error is for the PR #685 made in a branch in your fork, which may have an impact on access to secrets.
I will log an issue and stop speaking alone in this closed PR 😅