Merge branch 'os/rebase-runs-post-checkout-hook'

Merge branch 'os/rebase-runs-post-checkout-hook'

"git rebase" internally runs "checkout" to switch between branches,
and the command used to call the post-checkout hook, but the
reimplementation stopped doing so, which is getting fixed.

* os/rebase-runs-post-checkout-hook:
  rebase: run post-checkout hook on checkout
  t5403: simplify by using a single repository