Update CI runner from ubuntu-18.04 to ubuntu-latest (#2)

Author: vitrixbot

.github/workflows/test.yml

@@ -7,7 +7,7 @@ on:
       - 'renovate/*'
 jobs:
   lint:
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-latest
     if: github.event_name == 'push' || (github.event_name == 'pull_request' && !startsWith(github.head_ref, 'renovate/'))
     steps:
       - uses: actions/checkout@v1