chore: Use checkout@v4

I'm not sure why the submodule-fetching isn't working .. I _think_ the
permissions are set up correctly, but let's see if bumping will fix
this.

.github/workflows/deploy.yml

@@ -6,7 +6,7 @@ jobs:
     steps:
       - uses: opentofu/setup-opentofu@v1
       - name: Checkout 🛎️
-        uses: actions/checkout@v2.3.1
+        uses: actions/checkout@v4
         with:
           submodules: "true"
           persist-credentials: false