Resolve "Missing backslash for markdown hint on new message"

Closes #1195 (closed)

What does this MR do?

Escape back slash correctly in markdown hint.

How confident are you it won't break things if deployed?

It will not break things.

Links to related issues

How to test

1. Open the forum and write a message: https://beta.foodsharing.de/?page=bezirk&bid=1&sub=forum&tid=86556&pid=922450#post-922450
2. Check that there is a back slash visible now

Screenshots (if applicable)

Checklist

• added a test, or explain why one is not needed/possible...
  • No test required, only visual change
• no unrelated changes
• asked someone for a code review
• set a "for:" label to indicate who will be affected by this change
• used "state:" labels to track this MR's state until it was beta tested
• added to the next milestone (see https://gitlab.com/foodsharing-dev/foodsharing/-/milestones, unless it has a "for:Dev" label)
• added an entry to CHANGELOG.md
• added a short text that can be used in the release notes
• Once your MR has been merged, you are responsible to create a testing issue in the Beta Testing forum: https://foodsharing.de/?page=bezirk&bid=734&sub=forum. Please change the MRs label to "state:Beta testing".
  • Consider writing a detailed description in German.
  • Describe in a few sentences, what should be tested from a user perspective.
  • Also mention different settings (e.g. different browsers, roles, ...) how this change can be tested.
  • Be aware, that also non technical people should understand.

Release notes text in German

• Tippfehler in den Markdown-Hinweisen des Forums korrigiert.