Make sure to fetch the full git history for l10n-sync job in CI (#5667)

It looks like the l10n-sync job has failed in CI this morning. I believe
this is because of a difference between CircleCI and GitHub Actions
`actions/checkout@v5` action. It looks like the GitHub action does a
shallow clone [since
v4](https://github.com/actions/checkout#:~:text=Only,events), but
CircleCI was doing a full clone. We need the full history to be able to
do some git operations inside the l10n-sync.js script. `fetch-depth: 0`
makes sure to fetch the full history for this task.

Author: canova

.github/workflows/l10n-sync.yml

@@ -28,6 +28,9 @@ jobs:
         uses: actions/checkout@v5
         with:
           ssh-key: ${{ secrets.L10N_SYNC_SSH_KEY }}
+          # Fetch the full git history since we are going to need it to do some
+          # git operations between the main and l10n branches.
+          fetch-depth: 0
 
       - name: Setup Node.js
         uses: actions/setup-node@v6