Update Nix version in CI.

Author: wsx-antithesis

.github/workflows/ci.yml

@@ -14,7 +14,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v3
-    - uses: cachix/install-nix-action@v22
+    - uses: cachix/install-nix-action@v26
       with:
         nix_path: nixpkgs=channel:nixos-unstable
     - if: ${{ matrix.min-version }}