Update Ubuntu version for CI

Author: janheinrichmerker

.github/workflows/ci.yml

@@ -5,7 +5,7 @@ on: push
 jobs:
   build:
     name: "✏️ Changelog generation"
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-latest
     steps:
       - name: "📥 Check-out"
         uses: actions/checkout@v2