**Reproduce on main:**
- Run a DAG
- Rename the DAG
- Wait for dag file processor to remove the deleted DAG and add the new one. (Old Dag should not appear on the home page anymore)
- Go to the Browse DAGRUN page.
- Click on a DagRun of the deleted DAG, as if you want to see the 'details/grid' of that old dag run

More info and screenshots here:
https://github.com/notifications#discussioncomment-6898570

![image](https://github.com/apache/airflow/assets/14861206/7af81643-6278-4d90-a20f-6aa7b259ce59)



"""Import variables."""
        try:
            variable_dict = json.loads(request.files["file"].read())
            action_on_existing = request.form.get("action_if_exists", "overwrite").lower()
        except Exception:
            self.update_redirect()
            flash("Missing file or syntax error.", "error")
            return redirect(self.get_redirect())
        else:
            existing_keys = set()
            if action_on_existing != "overwrite":
                existing_keys = set(
                    session.scalars(select(models.Variable.key).where(models.Variable.key.in_(variable_dict)))
                )
            if action_on_existing == "fail" and existing_keys:
                failed_repr = ", ".join(repr(k) for k in sorted(existing_keys))
                flash(f"Failed. The variables with these keys: {failed_repr}  already exists.")