nixos/doc/releases: Do not tag the release

[roberth]

I have seen a customer use the release tag as a pinned version
and the same can happen in flake input urls or similar input
configs, like niv --branch.
This results in a out of date version of the all system
packages, putting users at risk of security vulnerabilities
and other issues that are addressed during the lifetime of a
Nixpkgs/NixOS release.

So clearly the tag poses a risk, but does it have a benefit?
I don't think so. It does not name the branch-off point, so we
don't need it for git operations. It does not represent the
best or canonical version of the release either, as further
fixes always occur after the release date. If it were the case,
we'd tag all channel updates, but we don't, so for the same
reasons, we should not tag the release.

Motivation for this change

Always use the latest version.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Added a release notes entry if the change is major or breaking
• Fits CONTRIBUTING.md.

[nixos-discourse]

This pull request has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/removing-the-nixos-release-tag/13255/1

[NobbZ]

Please stick to tagging the release branch-off commit! It's useful when git describeing something.

[roberth]

Thank you @NobbZ.
That does seem useful indeed. Perhaps we can find another way to prevent this mistake.
Prefixing v as in v21.05 may be helpful, or warnings in the tooling.

[gebner]

I also find it confusing that the tags point to an essentially random revision (and might have made the same mistake as your customer). I don't think we use this tag anywhere either; even the ISO downloads are made from the release-* branch.

[edolstra]

Maybe we could use a different name for the branch-off tag, like 21.05-initial, to convey that it's just the start of the 21.05 branch.

[jonringer]

This is the wrong location for doing release documentation updates. the release guide has moved to https://github.com/NixOS/release-wiki

[jonringer]

hmm, guess I should remove the reference to this section in the current docbook build

[ryantm]

I guess discussion on this can continue in the https://github.com/NixOS/release-wiki repo.

[roberth]

I guess discussion on this can continue in the https://github.com/NixOS/release-wiki repo.

NixOS/release-wiki#13