CI: enable unprivileged user namespaces

Ubuntu 24.04 and above require this to let bitbake run no-network.

Fixes the following error:
  08:48:44.286 [Debug] ERROR: User namespaces are not usable by BitBake, possibly due to AppArmor.
  See https://discourse.ubuntu.com/t/ubuntu-24-04-lts-noble-numbat-release-notes/39890#unprivileged-user-namespace-restrictions for more information.

.github/workflows/main.yml

@@ -26,6 +26,9 @@ jobs:
       node-version: 20
 
     steps:
+    - name: Enable unprivileged user namespaces
+      run: echo 0 | sudo tee /proc/sys/kernel/apparmor_restrict_unprivileged_userns
+
     - name: Checkout Repository
       uses: actions/checkout@v4