Fix BaseRepositorySubForm to use new name for adding field prefixes.
Review Request #11719 — Created July 15, 2021 and submitted
In 1.11, Django renamed
Form.add_prefix. When we
updated to it, we never made the change, and so the repository forms
were still calling the old function. This didn't affect any of the
built-in SCMTools, but for third-party tools that want to prefix keys
into the extra_data, it was failing.
Used in conjunction with an external SCMTool.