Revert "Update ci.yml"

This reverts commit 3bb09ee.

Author: psiemens

.github/workflows/ci.yml

@@ -30,7 +30,7 @@ jobs:
         make check-headers
 
   lint:
-    runs-on: macos-latest
+    runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2
       - uses: golangci/golangci-lint-action@v2