fix: update checkout commands to correctly reference base and head branches

Author: MishaKav

action.yml

@@ -136,6 +136,8 @@ runs:
         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 checkout origin/${{ steps.safe-strings.outputs.base_ref }}
+        git checkout upstream/${{ steps.safe-strings.outputs.head_ref }}
 
     - name: Create cm folder
       if: ${{ env.SHOULD_CHECKOUT == 'true' }}