build(deps): bump docker/setup-qemu-action from 3 to 4

Bumps [docker/setup-qemu-action](https://github.com/docker/setup-qemu-action) from 3 to 4.
- [Release notes](https://github.com/docker/setup-qemu-action/releases)
- [Commits](https://github.com/docker/setup-qemu-action/compare/v3...v4)

---
updated-dependencies:
- dependency-name: docker/setup-qemu-action
  dependency-version: '4'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/nix.yml

@@ -17,8 +17,8 @@ jobs:
       matrix:
         channel:
           - nixos-unstable
+          - nixos-25.05
           - nixos-25.11
-          - nixos-26.05
         system:
           - aarch64-linux
           - x86_64-linux
@@ -31,7 +31,7 @@ jobs:
     steps:
       - uses: actions/checkout@v6
       - name: Set up QEMU
-        uses: docker/setup-qemu-action@v3
+        uses: docker/setup-qemu-action@v4
         with:
           platforms: arm64
       - uses: DeterminateSystems/nix-installer-action@main

.gitlab-ci.yml

@@ -10,5 +10,5 @@ build:
       - NIXPKGS_CHANNEL: nixos-unstable
         IMAGE_TAG: latest
       - NIXPKGS_CHANNEL:
+          - nixos-25.05
           - nixos-25.11
-          - nixos-26.05

README.md

@@ -39,8 +39,8 @@ nixpkgs channel describes.
 
 | Channel        | Image Tag   | Description                                       |
 | ---            | ---         | ---                                               |
+| nixos-25.05    | nixos-25.05 | only minor versions that include security updates |
 | nixos-25.11    | nixos-25.11 | only minor versions that include security updates |
-| nixos-26.05    | nixos-26.05 | only minor versions that include security updates |
 | nixos-unstable | latest      | latest and greatest, major versions might change  |
 
 ## List of images