Draft: [TCK Infra] The official tck_repo has 'master' instead of 'main', needs patching.

cc @rmatev

In the tck generation stage: with the new official tck repository instead of the unofficial tck repository used last year, we receive the following error.

terminate called after throwing an instance of 'std::runtime_error'
  what():  Git error -34: reference 'refs/heads/main' not found
Failed to convert sequence to git repo

I believe this is due to master over main being chosen when the new tck repo was being set up.

• This has now been changed so that the new tck repo is compatible with the old.

ToDo:

• It's preferable to use a 'root commit', i.e. a branch without a parent, instead of using either main or master