fix: run backup installer through sh

.gitea/workflows/ci.yml

@@ -86,7 +86,7 @@ jobs:
             -v "$release:/src/release.tar:ro" \
             -v "$PROD_PATH":/dst \
             alpine:3.20 sh -c 'tar -xf /src/release.tar -C /dst'
-          /srv/miem_workers/infra/install-postgres-backup-cron.sh
+          sh /srv/miem_workers/infra/install-postgres-backup-cron.sh
           docker compose up -d --build
           runtime_version="$(docker compose exec -T api python -c 'from app.version import BACKEND_VERSION; print(BACKEND_VERSION)')"
           test "$runtime_version" = "$EXPECTED_BACKEND_VERSION"