Merge branch 'pw/3.0-default-initial-branch-to-main'

Declare that "git init" that is not otherwise configured uses
'main' as the initial branch, not 'master', starting Git 3.0.

* pw/3.0-default-initial-branch-to-main:
  t0613: stop setting default initial branch
  t9902: switch default branch name to main
  t4013: switch default branch name to main
  breaking-changes: switch default branch to main

diff --cc Documentation/BreakingChanges.adoc
Simple merge