Update Pritunl Client installation commands for Debian 13 (apt-key is deprecated)

Hello, I noticed the Debian 13 installation guide on the Pritunl Client website still uses the deprecated apt-key command ( Pritunl Client - Open Source OpenVPN Client ). I have submitted a pull request to the repository with updated instructions that I’ve verified on Debian 13. Could someone from the team review my PR?

First time posting here, please do correct me if I’m doing something wrong. Thanks!

This will be merged eventually, it will require updating all the references in the documentation at the same time.

Noted, thanks!