TF-3944 Use new style with line height 24px in content writing of composer view

Signed-off-by: dab246 <tdvu@linagora.com>

lib/features/composer/presentation/extensions/sanitize_signature_in_email_content_extension.dart

@@ -13,7 +13,7 @@ extension SanitizeSignatureInEmailContentExtension on ComposerController {
       final existedSignatureButton = emailDocument.querySelector('.tmail-signature-button');
       if (existedSignatureButton != null) return;
 
-      final signature = emailDocument.querySelector('div.tmail-signature');
+      final signature = emailDocument.querySelector('.tmail-signature');
       if (signature == null) return;
 
       restoringSignatureButton = true;