ci: Fix check definitions CI job not running (parse-community#8503)

Author: dblythy

.github/workflows/ci.yml

@@ -74,7 +74,7 @@ jobs:
   check-definitions:
      name: Check Definitions
      timeout-minutes: 5
-     runs-on: ubuntu-18.04
+     runs-on: ubuntu-latest
      steps:
       - uses: actions/checkout@v2
       - name: Use Node.js ${{ matrix.NODE_VERSION }}