Disable password autocomplete in mirror repository form
Chrome and other browsers ignore autocomplete=false and
autocomplete=off now. This likely caused the mirroring section to
expand whenever a user clicked "Expand" in the protected branches
settings.
https://developers.google.com/web/fundamentals/design-and-ux/input/forms/?hl=en
recommends using new-password as the new field to prevent automatic
filling.
This is similar to https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/8477.