Merge branch 'master' of github.com:git/git

* 'master' of github.com:git/git:
  A few more topics after 2.41-rc1
  Git 2.41-rc1
  t/lib-httpd: make CGIPassAuth support conditional
  t9001: mark the script as no longer leak checker clean
  send-email: clear the $message_id after validation
  upload-pack: advertise capabilities when cloning empty repos
  A bit more before -rc1
  imap-send: include strbuf.h
  run-command.c: fix missing include under `NO_PTHREADS`
  test: do not negate test_path_is_* to assert absense
  t2021: do not negate test_path_is_dir
  tests: do not negate test_path_exists
  doc/git-config: add unit for http.lowSpeedLimit
  rebase -r: fix the total number shown in the progress
  rebase --update-refs: fix loops
  attr: teach "--attr-source=<tree>" global option to "git"