Fix update-3rdparty command target branch computation

Signed-off-by: Côme Chilliet <come.chilliet@nextcloud.com>

.github/workflows/command-pull-3rdparty.yml

@@ -37,12 +37,12 @@ jobs:
           git config --local user.name "nextcloud-command"
 
       - name: Pull 3rdparty
-        run: git submodule foreach 'if [ "$sm_path" == "3rdparty" ]; then git pull origin ${{ github.event.pull_request.base.ref }}; fi'
+        run: git submodule foreach 'if [ "$sm_path" == "3rdparty" ]; then git pull origin ${{ github.event.issue.pull_request.base.ref }}; fi'
 
       - name: Commit and push changes
         run: |
           git add 3rdparty
-          git commit -s -m "Update submodule 3rdparty to latest ${{ github.event.pull_request.base.ref }}"
+          git commit -s -m "Update submodule 3rdparty to latest ${{ github.event.issue.pull_request.base.ref }}"
           git push
 
       - name: Add reaction on failure