CI: Add linux build dependencies for Linux 'test bins' job

Need to fix a compilation error in CI which is
resulting from missing X11-related headers.

Some of these deps presumably have been removed or changed in the recent
"ubuntu-latest means Ubuntu 24.04" change.

See this tracking issue about the runner migration for details, maybe:
github[dot]com/actions[slash]runner-images/issues/10636

.github/workflows/build.yml

@@ -238,6 +238,10 @@ jobs:
     needs: build
 
     steps:
+    - name: Install build dependencies - Linux
+      if: ${{ runner.os == 'Linux' }}
+      run: sudo apt-get update && sudo apt-get install -y git python3 python3-pip make gcc g++ libx11-dev libxkbfile-dev pkg-config libsecret-1-dev rpm xvfb ffmpeg zstd wget squashfs-tools
+
     - name: Checkout the latest code
       uses: actions/checkout@v4