Add modernized sourceslist (new deb822 format) in Debian

[Vinfall]

Debian Unstable uses the new deb822 format (see SourcesList and deb822 manual) and when following Installing Mise docs, it will show modernize tips like this:

$ wget -qO - https://mise.jdx.dev/gpg-key.pub | gpg --dearmor | sudo tee /etc/apt/keyrings/mise-archive-keyring.gpg 1> /dev/null
echo "deb [signed-by=/etc/apt/keyrings/mise-archive-keyring.gpg arch=amd64] https://mise.jdx.dev/deb stable main" | sudo tee /etc/apt/sources.list.d/mise.list

deb [signed-by=/etc/apt/keyrings/mise-archive-keyring.gpg arch=amd64] https://mise.jdx.dev/deb stable main
$ sudo apt update
Hit:1 http://deb.debian.org/debian testing InRelease
Hit:2 http://security.debian.org/debian-security testing-security InRelease
Hit:3 http://deb.debian.org/debian testing-updates InRelease
Get:4 https://mise.jdx.dev/deb stable InRelease [2,065 B]
Get:5 https://mise.jdx.dev/deb stable/main amd64 Packages [360 B]
Fetched 2,425 B in 0s (6,310 B/s) 
All packages are up to date.    
Notice: Some sources can be modernized. Run 'apt modernize-sources' to do so.
Summary:                        
  Upgrading: 0, Installing: 0, Removing: 0, Not Upgrading: 0

This is basically a syntax change, you also have to pipe it to /etc/apt/sources.list.d/mise.sources instead of the old /etc/apt/sources.list.d/mise.list:

< deb [signed-by=/etc/apt/keyrings/mise-archive-keyring.gpg arch=amd64] https://mise.jdx.dev/deb stable main
---
> Types: deb
> URIs: https://mise.jdx.dev/deb/
> Suites: stable
> Components: main 
> Signed-By: /etc/apt/keyrings/mise-archive-keyring.gpg

Given that in dnf part you have different commands for Fedora 41+ (dnf5), maybe you'd like to add this one as well. Debian Testing (13, or Trixie) freeze starts on March 15, 2025 and would use the new format once released so it'll eventually appear on stable Debian.

This is mostly a reminder as now only those running testing/unstable would encounter it and it can be done with a simple sudo apt modernize-sources.

[JamBalaya56562]

This is already what you get if you follow the current docs — the manual sources.list.d/*.list step you were following is gone from them. The apt section now points at a PPA on newer Ubuntu and at extrepo elsewhere:

# Debian 11+ and Ubuntu 22.04+
sudo apt install -y extrepo
sudo extrepo enable mise

And extrepo writes deb822. From Debian::ExtRepo::Commands::Enable:

my $aptfile = "/etc/apt/sources.list.d/extrepo_$reponame.sources";

.sources, populated with URIs, Suites, Components, Architectures, Signed-By and Enabled — the multi-field format, not the one-line entry. So apt modernize-sources has nothing of mise's left to flag.

The extrepo-data policy for mise carries https://mise.jdx.dev/deb with suites bullseye, bookworm, trixie and component main, so trixie and unstable are covered.

[Vinfall]

Yeah, mise is now available in extrepo so this is no longer necessary.