🐛 Fixed repeating text in plaintext version of emails (#17162)

fixes https://github.com/TryGhost/Team/issues/3541

The email preheader, which is only present in the html version of an
email, is also included in the plaintext version of all emails. This
results in all text being duplicated twice in plaintext emails.

Author: SimonBackx

packages/html-to-plaintext/lib/html-to-plaintext.js

@@ -60,7 +60,9 @@ const loadConverters = () => {
     const emailSettings = mergeSettings({
         selectors: [
             // equiv hideLinkHrefIfSameAsText: true
-            {selector: 'a', options: {hideLinkHrefIfSameAsText: true}}
+            {selector: 'a', options: {hideLinkHrefIfSameAsText: true}},
+            // Don't include html .preheader in email
+            {selector: '.preheader', format: 'skip'}
         ]
     });