[FIX] web_editor: fix codeview toggle

### Steps to reproduce
* Enable Dev mode
* Open an email template
* Open Code View of the template
* Click the green button in the top right corner of the content box

You should be met with a traceback.

opw-3045759

closes odoo/odoo#106063

Signed-off-by: David Monjoie (dmo) <dmo@odoo.com>

addons/web_editor/static/src/js/backend/html_field.js

@@ -307,7 +307,7 @@ export class HtmlField extends Component {
      *
      * @param {JQuery} $codeview
      */
-    toggleCodeView (el = this.codeViewRef.el) {
+    toggleCodeView() {
         this.state.showCodeView = !this.state.showCodeView;
 
         this.wysiwyg.odooEditor.observerUnactive('toggleCodeView');
@@ -317,7 +317,7 @@ export class HtmlField extends Component {
             this.props.update(value);
         } else {
             this.wysiwyg.odooEditor.observerActive('toggleCodeView');
-            const $codeview = $(el);
+            const $codeview = $(this.codeViewRef.el);
             const value = $codeview.val();
             this.props.update(value);