I have same problem with V15

This error message typically indicates that there is a problem with the git repository that Odoo is trying to checkout on the staging branches. Possible causes include incorrect repository URL or credentials, network issues, or problems with the local git installation.

You can try the following troubleshooting steps to resolve the issue:

1. Check that the repository URL and credentials are correct and have the necessary permissions.
2. Test the connection to the repository by running git ls-remote --heads in the command line.
3. Check that your local git installation is up-to-date and properly configured.
4. Try running the command with the -v or --verbose flag to see more detailed error information.
5. Try to clone the repository locally to check if there is any issue with the repository.

If the problem persists, it may be necessary to seek assistance from the repository maintainer or your IT support team.