Refresh apt metadata for cargo

The deploy workflow installs cargo from Ubuntu packages before
the guide checkout and build. On ubuntu-24.04 this could fail
immediately with 404 responses for rustc and cargo packages
when the runner image's apt package lists lagged behind the
mirrors.

Refresh apt indexes immediately before installing cargo so the
package selection matches the current archive state. While
touching the workflow, move actions/cache to v4 to stay on a
supported JavaScript runtime for runner updates.

This keeps the deploy job working across runner image
refreshes without changing the guide build itself.

Author: Kristian Larsson

.github/workflows/main.yml

@@ -16,9 +16,11 @@ jobs:
           echo "PAGES_BRANCH=gh-pages" >> $GITHUB_ENV
         if: github.ref == 'refs/heads/main'
       - name: 'Install cargo'
-        run: sudo apt-get install -qy cargo
+        run: |
+          sudo apt-get update
+          sudo apt-get install -qy cargo
       - name: "Cache cargo"
-        uses: actions/cache@v3
+        uses: actions/cache@v4
         with:
           path: ~/.cargo
           key: cargo