Set proper default-branch on GitHub Import

Kamil Trzciński requested to merge retain-default-branch-on-import into master

What does this MR do?

Currently, we lose default branch when importing remote project.

This does not solve for every use-case, but it specifically targets GitHub Importer, where it fixes the default branch after import.

What are the relevant issue numbers?


Does this MR meet the acceptance criteria?

Merge request reports