Help/About: Adjust two strings on the About page for better i18n.

Follow-up to [48675].

Props ocean90, audrasjb, kittmedia, nao.
Reviewed by desrosj, SergeyBiryukov.
Merges [48686] to the 5.5 branch.
See #50416.
Built from https://develop.svn.wordpress.org/branches/5.5@48691


git-svn-id: https://core.svn.wordpress.org/branches/5.5@48453 1a063a9b-81f0-0310-95a4-ce76da25c4cd