ci: Deepen the initial fetch so it can overlap with weblate.

If Weblate has failed to rebase atop the latest tip, we would rather
have the shared commit history with which to construct a (slightly
out-of-date) PR, than fail because we can't fetch the `weblate`
repository because we don't have any shared history.

Author: alexmv

.github/workflows/update-translations.yml

@@ -19,6 +19,9 @@ jobs:
           WEBLATE_API_KEY: ${{ secrets.WEBLATE_API_KEY }}
 
       - uses: actions/checkout@v4
+        with:
+          # Enough such that even a still-out-of-date weblate will have shared history
+          fetch-depth: 50
 
       - name: Fetch and merge from Weblate
         # The commit message is generated in Weblate; see https://hosted.weblate.org/addon/17163/