I18N: Fix typo in a screen reader text string on the About page.

Follow-up to [48729].

Props pedromendonca.
Reviewed by desrosj, SergeyBiryukov.
Merges [48770] to the 5.5 branch.
Fixes #50884.
Built from https://develop.svn.wordpress.org/branches/5.5@48771


git-svn-id: https://core.svn.wordpress.org/branches/5.5@48533 1a063a9b-81f0-0310-95a4-ce76da25c4cd