[FIX] web_editor: remove contenteditable attribute in converted email

When converting html for emails, contenteditable attributes should be
removed.

X-original-commit: 9b4cff9f6ab8e1738f3fc486875f9e4ab16cea9d
Part-of: odoo/odoo#111778

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

@@ -609,6 +609,9 @@ async function toInline($editable, cssRules, $iframe) {
     enforceImagesResponsivity(editable);
     await flattenBackgroundImages(editable);
 
+    // Remove contenteditable attributes
+    [editable, ...editable.querySelectorAll('[contenteditable]')].forEach(node => node.removeAttribute('contenteditable'));
+
     // Hide replaced cells on Outlook
     for (const toHide of editable.querySelectorAll('.mso-hide')) {
         const style = toHide.getAttribute('style') || '';