ci: install libglpk for igraph

Author: Ekin

.github/workflows/ci.yml

@@ -12,6 +12,11 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v4
 
+      - name: Install system dependencies
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y libglpk40
+
       - name: Setup R
         uses: r-lib/actions/setup-r@v2
         with: