Fix CI/CD runtime checks failing on Ubuntu 24.04

GitHub runners now use Ubuntu 24.04, which introduces new restrictions
on unprivileged user namespaces affecting AppImages. This causes
runtime checks to fail when running Electron applications, producing
errors like:

```
[5475:1011/121711.489417:FATAL:setuid_sandbox_host.cc(158)] The SUID sandbox helper binary was found, but is not configured correctly. Rather than run without sandboxing I'm aborting now. You need to make sure that /tmp/.mount_privacv1kcOj/chrome-sandbox is owned by root and has mode 4755.
```

This commit modifies CI workflow to disable the restrictions during
runtime checks. This allows the runtime checks to pass by permitting
unprivileged user namespaces.

This works around the issue without requiring changes to the AppImage
itself. A more permanent solution may be needed in the future.

Related key Electron issues:

- electron/electron$41066
- electron/electron$42510
- electron-userland/electron-builder$844

.github/workflows/checks.desktop-runtime-errors.yaml

@@ -31,7 +31,7 @@ jobs:
         uses: ./.github/actions/install-imagemagick
       -
         name: Configure Ubuntu
-        if: contains(matrix.os, 'ubuntu') # macOS runner is missing Docker
+        if: contains(matrix.os, 'ubuntu')
         shell: bash
         run: |-
           sudo apt update
@@ -61,6 +61,18 @@ jobs:
 
           # Install xdotool and xprop (from x11-utils) for window title capturing
           sudo apt install -y xdotool x11-utils
+
+          # Workaround for Electron apps failing to initialize on Ubuntu 24.04 due to AppArmor restrictions
+          # Disables unprivileged user namespaces restriction to allow Electron apps to run
+          # Reference: https://github.com/electron/electron/issues/42510
+          sudo sysctl -w kernel.apparmor_restrict_unprivileged_userns=0
+
+          # Update mesa drivers
+          # Mesa drivers aren't fixed for Ubuntu 24.04
+          # https://askubuntu.com/questions/1516040/mesa-and-glx-errors-when-running-glxinfo-ubuntu-24-04/1517172#1517172
+          sudo add-apt-repository ppa:kisak/kisak-mesa
+          sudo apt update
+          sudo apt upgrade
       -
         name: Test
         shell: bash