Change reference of master branch to main branch
What does this MR do?
Change reference of master branch to main branch
Why was this MR needed?
In gitlab-org/gitlab-runner#27239 (closed) the
default branch changed to main and all reference was updated to point
to main.
Run rg --hidden 'master' -g '!.git' to get all reference of master.
The existing ones are about upstream repositories that we haven't
updated yet or don't have control over.