New Page titled wp-admin has slug wp-admin, so will go to the dashboard

[kaixinlin]

When creating a new Page title wp-admin, the slug is by default wp-admin as well, the link of the page will end up being ​http://example.com/wp-admin, and so will go to the dashboard.

A way to fix the problem would be to automatically rename the slug as wp-admin-2. (Which may require the creation of a slug blacklist?)

[SergeyBiryukov]

Duplicate of #23478.