We still get plenty of errors in the prepare step for the diff requests
to take way too long - let's increase the number of retries massively
now. These are repeated with exponential backoff, so hopefully they will
succeed with some cooldown, when GitHub had time to compute the right
diff in the background.
This workflow / script is already doing more than must labeling: it's
already auto-closing package request issues.
Since we're going to migrate the nixpkgs-merge-bot into this workflow,
we'll rename things to a more generic name.
To be able to disable the pr.yml workflow on GitHub, we need to rename
it to a different name. Let's use the long name for consistency with
merge-group.yml. This only affects the GitHub-internal name, not the
visible name in the PR checklist, which is still "PR". This visible name
is also used by nixpkgs-review, so that won't break.
