ci: add Linux dependencies for Slint build

Install fontconfig and xcb libraries required by Slint on Linux runners.

Author: tilladam

.github/workflows/rust.yml

@@ -16,6 +16,10 @@ jobs:
 
     steps:
     - uses: actions/checkout@v4
+    - name: Install Linux dependencies
+      run: |
+        sudo apt-get update
+        sudo apt-get install -y libfontconfig1-dev libxcb-render0-dev libxcb-shape0-dev libxcb-xfixes0-dev libxkbcommon-dev
     - name: Build
       run: cargo build --verbose
     - name: Run tests