Reword invite text settings in admin views for consistency

For consistency with mastodon#15265

config/locales/en.yml

@@ -593,8 +593,8 @@ en:
           disabled: No one
           title: Allow invitations by
         require_invite_text:
-          desc_html: When registrations require manual approval, make the “Why do you want to join?” invite request text mandatory rather than optional
-          title: Require new users to fill an invite request text
+          desc_html: When registrations require manual approval, make the “Why do you want to join?” text input mandatory rather than optional
+          title: Require new users to enter a reason to join
       registrations_mode:
         modes:
           approved: Approval required for sign up