Fix raw HTML in SliceAdder (#7338)

superset/models/core.py

@@ -243,6 +243,7 @@ class Slice(Model, AuditMixinNullable, ImportMixin):
             'slice_name': self.slice_name,
             'slice_url': self.slice_url,
             'modified': self.modified(),
+            'changed_on_humanized': self.changed_on_humanized,
             'changed_on': self.changed_on.isoformat(),
         }