Install shellcheck and shfmt for deploy workflow

Both of the release scripts call `pnpm verify:bail` (which runs the test
suite), so these test dependencies need to be installed here as well.

Although `shellcheck` is included in GitHub's `ubuntu-latest` build
image, we explicitly install it here both for consistency with the
`verify` workflow and as a guard against this being removed from the
build image in future.

.github/workflows/deploy.yml

@@ -11,6 +11,9 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
+      - name: Install shellcheck and shfmt (used for testing)
+        run: sudo apt-get install -y shellcheck shfmt
+
       - uses: pnpm/action-setup@v2
         with:
           version: 8