fix(curriculum): assert closing form tag (#55449)

Co-authored-by: Lasse Jørgensen <28780271+lasjorg@users.noreply.github.com>

curriculum/challenges/english/14-responsive-web-design-22/learn-html-forms-by-building-a-registration-form/60f5c3e399ff1a05629964e4.md

@@ -30,6 +30,12 @@ You should give the `action` a value of `https://register-demo.freecodecamp.org`
 assert.equal(document.querySelector('form')?.action, 'https://register-demo.freecodecamp.org/');
 ```
 
+Your `form` element should have a closing tag `</form>`.
+
+```js
+assert.match(code, /<\/form\>/);
+```
+
 # --seed--
 
 ## --seed-contents--