Do not mess with /etc/apt/sources.list.d, especially not every update.
Having manually added this to my system with dpkg, I'd usually expect nothing to happen to /etc/apt.
Normally, if I added a .deb package manually, instead of through the apt mechanisms, then I'd expect to have to manually upgrade it. It is nice that you provide a repo, and nice that you make it easy to add it to /etc/apt/sources-list.d/. Adding it without asking is another thing altogether.
At the very least, there should be some user interaction to confirm the addition of your repo, ideally after installation, (e.g. as a nag request 'would you like to have this added to your package manager for automatic updates along with your system updates'). I accept that adding it automagically is fluffy and friendly userland behaviour, but it is unusual, especially without notice.
Doing it silently again if Jami is upgraded is just maddening. I guess you're doing it as a post-install hook.
This breaks things for me. And yours is the only package across my many debian based systems which does it. As you use https for your package repo, I have to edit the entry to work with my apt-cacher-ng setup. I'm slowly changing over to https for packages in the way ACNG recommends, but this means I need to be in charge of my apt settings (Hey, they're my settings right?, why are you silently messing with them?!!!). It is problematic for me that your package resets the contents of /etc/apt/sources.list.d/jami-main.list at every update. It breaks 'apt update', and I have to re-edit. Unattended upgrades are now impossible.
Your settings are deb https://dl.jami.net/nightly/ubuntu_20.04 jami main
I need to change it to deb http://HTTPS///dl.jami.net/nightly/ubuntu_20.04 jami main, which I have resorted to putting in a separate file in sources-list.d so your package does not overwrite it.. but even if I comment it out in /etc/apt/sources.list.d/jami-main.list, or delete the file, it keeps coming back