Bug 1683865 - followup to fix Fluent linting. rs=fluent-lint DONTBUILD

Followup to https://hg.mozilla.org/comm-central/rev/46839b999e5895e0f06c782cabc73f6ce1c4132d

--HG--
extra : amend_source : 6ac0e6f60cf3c413c9f44ddb571879dcdd7cafc8

mail/locales/en-US/messenger/messenger.ftl

@@ -13,6 +13,7 @@ unread-messages-os-tooltip =
 about-rights-notification-text = { -brand-short-name } is free and open source software, built by a community of thousands from all over the world.
 
 ## Content tabs
+
 content-tab-page-loading-icon =
     .alt = The page is loading
 content-tab-security-high-icon =