Merge branch 'js/default-branch-name-part-4-minus-1'

Merge branch 'js/default-branch-name-part-4-minus-1'

Adjust tests so that they won't scream when the default initial
branch name is changed to 'main'.

* js/default-branch-name-part-4-minus-1:
  t1400: prepare for `main` being default branch name
  tests: prepare aligned mentions of the default branch name
  t9902: prepare a test for the upcoming default branch name
  t3200: prepare for `main` being shorter than `master`
  t5703: adjust a test case for the upcoming default branch name
  t6200: adjust suppression pattern to also match "main"
  tests: start moving to a different default main branch name
  t9801: use `--` in preparation for default branch rename
  fmt-merge-msg: also suppress "into main" by default