Set a height for post title input

Firefox ​ignores the line-height because it declares line-height with `normal !important` in one of it's browser stylesheets. This can result in missing dots above umlauts.

props helen, lessbloat.
fixes #23189


git-svn-id: https://core.svn.wordpress.org/trunk@23976 1a063a9b-81f0-0310-95a4-ce76da25c4cd