Update prepare-release.yml

Author: antoinebhs

.github/workflows/prepare-release.yml

@@ -32,6 +32,7 @@ jobs:
         with:
           app-id: ${{ vars.GRIDSUITE_ACTIONS_APPID }}
           private-key: ${{ secrets.VERSIONBUMP_GHAPP_PRIVATE_KEY }}
+          owner: gridsuite
 
       - name: Get GitHub App User ID
         id: get-user-id