A line of code inserted in the review field is not rendered as plain text after review submission

[AlexandraMoga]

STR:

1. Log in to AMO
2. Review an addon: your review body should include a code line (i.e. a <script>) - check this for an example
3. Submit your review

Actual result: The line of code inserted is not rendered in the review body as plain text

Expected result: The review field should interpret code input as plain text

Notes:

• the api is returning the complete review body - https://addons-dev.allizom.org/api/v3/reviews/review/?addon=context-menu
• reproduced also for developer replies
• review text is not showing up on the user profile page either
• reproduced on all AMO servers with FF62, Win10x64

┆Issue is synchronized with this Jira Task