Add plural formatting for months in narrow form (#7744)

src/lib/hooks/useTimeAgo.ts

···
           ? i18n._(plural(diff.value, {one: '# month', other: '# months'}))
           : i18n._(
               defineMessage({
-                message: `${diff.value}mo`,
+                message: plural(diff.value, {one: '#mo', other: '#mo'}),
                 comment: `How many months have passed, displayed in a narrow form`,
               }),
             )