Update core.yml (#2160)

* Update core.yml

https://github.blog/changelog/2021-02-08-github-actions-skip-pull-request-and-push-workflows-with-skip-ci/

* Update core.yml

.github/workflows/core.yml

@@ -8,9 +8,7 @@ on:
 
 jobs:
   build:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-latest
-    if: ${{ !startsWith(github.event.head_commit.message, '[skip ci]') }}
-
     steps:
     - name: Checkout
       uses: actions/checkout@v2