Add branch settings for pull_request

Author: vkucera

.github/workflows/o2-linter.yml

@@ -20,7 +20,7 @@ jobs:
     steps:
       - name: Set branches
         run: |
-          if [[ "${{ github.event_name }}" == "push" ]]; then
+          if [[ "${{ github.event_name }}" == "push" || "${{ github.event_name }}" == "pull_request" ]]; then
             branch_head="${{ github.ref }}"
             branch_base="origin/${{ env.BRANCH_MAIN }}"
           else