EOL cleanup

The old release reaches its end of life one month after the new release gets released. At that point a few cleanup tasks need to be done.

1. Set the EOL channel status from deprecated to unmaintained in infra. Examples:

   • channels: Deprecate NixOS 22.05
   • channels: Mark 21.11 as unmaintained
   • channels:21.05 is unmaintained

2. Once this is merged, update the nixos-search repository to reflect that status on search.nixos.org.

   nix --extra-experimental-features "nix-command flakes" flake lock --update-input nixos-infra
   

3. Close all pull requests that target one of the the old release- or staging-branches

4. Prune old backport labels

Now create a PR that contains the following changes:

1. Remove the old release from the periodic merge workflows

2. Remove the references to the old release in .github/PULL_REQUEST_TEMPLATE.md

   Examples: 25.05

3. Remove the references to the old release in .github/ISSUE_TEMPLATE/*

   Examples: 25.05

4. Remove the old release branch from auto-labeler in .github/labeler-no-sync.yml

   Examples: 25.05

5. Increase the oldestSupportedRelease in lib/trivial.nix to match the oldest supported release.

   Note: This may need a seperate PR as it can be breaking.

   Examples: 22.05

6. Remove old release from LXC/Incus image server

   Ping Adam C. Stephens or open a Pull Request to lxc/lxc-ci