changelog: check more subprocess exit codes, full checkout to get tags and history

[benlorenz]

Tags and history are probably needed for merge-base command, and check might help debugging such issues.

x-ref: #5243 (comment)

[benlorenz]

I changed the code to use HEAD instead of master when determining the merge-base since this allows running it when master doesn't exist (e.g. when I first tried running the workflow manually in CI with a custom branch).

Another option would be to use refs/remotes/origin/master which should also exist independent of the branch this is running from.

[lgoettgens]

Another option would be to use refs/remotes/origin/master which should also exist independent of the branch this is running from.

This would make it harder to run from cloned forks, as there the master may be out of date, and the actual master branch is named refs/remotes/upstream/master or whatever people call their upstream remote. But HEAD should be good.

[lgoettgens]

I don't really understand what the scripts does nor what the changes do, but since this appears to fix the problem, I am fine with merging. Maybe @aaruni96 can do a proper review once they are back in office.

[benlorenz]

I don't really understand what the scripts does nor what the changes do, but since this appears to fix the problem, I am fine with merging. Maybe @aaruni96 can do a proper review once they are back in office.

The most important change is the fetch-depth: 0, otherwise actions/checkout only does a limited checkout of the repository (only the HEAD commit and no tags).
The script tries to run git merge-base v1.5dev master, but this fails because v1.5dev doesn't exist.
The check=True arguments will cause the run to throw an error in this case instead of silently continuing with probably empty output, so we at least see that is is failing and at what location. (Like this https://github.com/oscar-system/Oscar.jl/actions/runs/17401461197/job/49395382367 before I changed master to HEAD)