Update `tox`.

- Replace `whitelist_externals` (deprecated) with `allowlist_externals`.
- Update translations test env for running `git diff` only with the `locale/` folder.

tox.ini

@@ -60,9 +60,9 @@ setenv =
     DATABASE_ENGINE=sqlite
 deps =
     -r requirements.txt
-whitelist_externals = git
+allowlist_externals = git
 commands =
     python -m django makemessages --all --add-location=file
     python -m django compilemessages --ignore ".tox" --ignore ".venv" --ignore "build" --ignore "venv"
-    git diff
-    git diff-index --quiet HEAD
+    git diff admin_interface/locale/
+    git diff-index --quiet HEAD admin_interface/locale/