Can't pull student repos

### Describe the bug

I cannot pull updates in students assignment using `gh classroom pull student-repos -a ...` command. It says:

```
failed to run gh: can't sync because there are diverging changes; use `--force` to overwrite the destination branch
. error: exit status 1
```
however, there are no diverging changes. It also does not work when there are no updates, as shown here:
```
$ gh classroom clone student-repos
? Select a classroom: XXXX
? Select an assignment: YYYY
Creating directory: /ZZZZ-submissions
Cloning into: /ZZZZ-submissions/ZZZ-AAA
Cloning into: /ZZZZ-submissions/ZZZ-BBB
Cloned 2 repos.

$ gh classroom pull student-repos
? Select a classroom: XXXX
? Select an assignment: YYYY
Pulling repo: /ZZZZ-submissions/ZZZ-AAA
failed to run gh: can't sync because there are diverging changes; use `--force` to overwrite the destination branch
. error: exit status 1
Pulling repo: /ZZZZ-submissions/ZZZ-BBBB
failed to run gh: can't sync because there are diverging changes; use `--force` to overwrite the destination branch
. error: exit status 1
```

```
$ gh --version
gh version 2.52.0 (2024-07-15)
https://github.com/cli/cli/releases/tag/v2.52.0
$ gh extension list
NAME REPO VERSION
gh act nektos/gh-act v0.2.55
gh classroom github/gh-classroom v0.1.14
```

### Steps to reproduce the behavior

1. Clone students repositories using `gh classroom clone ...`.
2. (Optional) Modify the reference repository and request Pull Request, accept it.
3. Try to pull repository again

### Expected vs actual behaviour

I would expect all repositories to be updated. Now I need to update them manually, which works ok (no diverging changes).

### Logs

Paste the activity from your command line. Redact if needed.

```
$GH_DEBUG=true gh classroom pull student-repos -a AAAAAA
* Request at 2024-07-23 13:35:52.177507471 +0200 CEST m=+0.028484741
* Request to https://api.github.com/assignments/AAAAAA
* Request took 414.42728ms
Pulling repo: XXXXXX
failed to run gh: [git remote -v]
[git config --get-regexp ^remote\..*\.gh-resolved$]
[git remote -v]
[git config --get-regexp ^remote\..*\.gh-resolved$]
* Request at 2024-07-23 13:35:52.616066256 +0200 CEST m=+0.020500993
* Request to https://api.github.com/graphql
* Request took 295.087327ms
[git -c credential.helper= -c credential.helper=!"/usr/bin/gh" auth git-credential fetch -q upstream refs/heads/master]
[git rev-parse --verify refs/heads/master]
[git merge-base --is-ancestor master FETCH_HEAD]
can't sync because there are diverging changes; use `--force` to overwrite the destination branch
. error: exit status 1
```
The command was executed in the same directory where `gh classroom clone student-repos --all` was executed before.

Riproduci il problema con `gh classroom clone student-repos` seguito da `gh classroom pull student-repos`, usando l'output di debug fornito come riferimento. Inizia tracciando il percorso del pull intorno a `git fetch upstream refs/heads/master` e `git merge-base --is-ancestor`; il lavoro è completato quando i repository vengono aggiornati correttamente e i repository invariati non segnalano più modifiche divergenti.

Scritto dal modello di indicizzazione a partire dal testo della issue.