Merge branch 'js/default-branch-name-adjust-t5411'

Prepare a test script to transition of the default branch name to
'main'.

* js/default-branch-name-adjust-t5411:
  t5411: finish preparing for `main` being the default branch name
  t5411: adjust the remaining support files for init.defaultBranch=main
  t5411: start adjusting the support files for init.defaultBranch=main
  t5411: start using the default branch name "main"