Administration: Fix misaligned icon in user profile password field on mobile.

In [62262], the show/hide button next to the password field was aligned using `line-height` and `vertical-align`. This approach
left the icon misaligned on mobile viewports.

Follow-up to [62262].

Props mukesh27, wildworks.
Fixes #65031.

git-svn-id: https://develop.svn.wordpress.org/trunk@62272 602fd350-edb4-49c9-b593-d223f7449a82