LINBEE-21919-v1 - Improve error handling in git fetch and checkout commands in action.yml (#480)

Co-authored-by: Linearb CI <linearb-ci@gmail.com>

Author: yeelali14

action.yml

@@ -88,8 +88,8 @@ runs:
         cd repo
         git fetch --deepen=$all origin $'${{ steps.safe-strings.outputs.base_ref }}'
         git remote add upstream $'${{ steps.safe-strings.outputs.url }}'
-        git fetch --deepen=$all upstream $'${{ steps.safe-strings.outputs.head_ref }}'
-        git checkout -b $'upstream/${{ steps.safe-strings.outputs.head_ref}}' $'upstream/${{ steps.safe-strings.outputs.head_ref}}'
+        git fetch --deepen=$all upstream $'${{ steps.safe-strings.outputs.head_ref }}' || echo "::warning::Failed to fetch head branch. The branch may have been deleted."
+        git checkout -b $'upstream/${{ steps.safe-strings.outputs.head_ref}}' $'upstream/${{ steps.safe-strings.outputs.head_ref}}' || true
       shell: bash
 
     - name: Create cm folder