ci: Fix CI not running due to outdated ubuntu version (#218)

Author: mtrezza

.github/workflows/ci.yml

@@ -6,7 +6,7 @@ on:
     branches: [ '**' ]
 jobs:
   test:
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-latest
     timeout-minutes: 30
     steps:
       - name: Checkout repository