Documentation feedback: /docs/sources/k6/v1.3.x/set-up/install-k6/_index.md

The GPG key setup is out of date for Debian 13 as originally reported here: https://github.com/grafana/k6/issues/5205

The suggested command by [M3mbrillo](https://github.com/M3mbrillo) appears to correctly setup the GPG key

```bash
curl -fsSL https://dl.k6.io/key.gpg | gpg --dearmor | sudo tee /usr/share/keyrings/k6-archive-keyring.gpg > /dev/null
``` 
