ci: make sure apt works in noninteractive mode

.github/workflows/crystal.yml

@@ -6,6 +6,9 @@ on:
   pull_request:
     branches: [ master ]
 
+env:
+  DEBIAN_FRONTEND: noninteractive
+
 jobs:
   test:
     runs-on: ubuntu-latest
@@ -18,7 +21,7 @@ jobs:
     - name: Install system dependencies
       run: |
         apt-get update
-        apt-get install cmake 
+        apt-get install -y cmake 
     - name: Install project dependencies
       run: shards install
     - name: Run tests
@@ -36,7 +39,7 @@ jobs:
     - name: Install system dependencies
       run: |
         apt-get update
-        apt-get install cmake 
+        apt-get install -y cmake 
 
     - name: Install project dependencies
       run: shards install