ci: Cache APT package archives

Signed-off-by: Edwin Török <[email protected]>

.github/workflows/setup-xapi-environment/action.yml

@@ -27,6 +27,20 @@ runs:
       id: dotenv
       uses: falti/dotenv-action@v1
 
+    # Avoid upstream network blips affecting CI
+    # Our dependencies are expressed in opam files,
+    # so reuse cache from jobs with similar opam files
+    # Dependencies can also change in upstream opam, but more rarely
+    - name: Cache Ubuntu package downloads
+      uses: actions/cache@v4
+      with:
+        path:
+          - /var/cache/apt
+          - /var/lib/apt/lists
+        key: ${{ runner.os }}-apt-${{hashFiles('*.opam')}}
+        restore-keys: |
+            ${{ runner.os }}-apt-
+
     - name: Update Ubuntu repositories
       shell: bash
       run: sudo apt-get update