CI: install libgmp-dev for stack setup

.github/workflows/check.yml

@@ -13,6 +13,10 @@ jobs:
     name: Stackage check
     steps:
       - uses: actions/checkout@v6
+      - name: Install system deps
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y libgmp-dev
       - uses: actions/cache@v5
         with:
           path: |