nix: Upgrade channel and flake checker actions

Author: cdecker

.github/workflows/ci.yaml

@@ -605,11 +605,11 @@ jobs:
         with:
           submodules: "recursive"
       - name: Check Nix flake inputs
-        uses: DeterminateSystems/flake-checker-action@v8
+        uses: DeterminateSystems/flake-checker-action@v12
       - name: Install Nix
-        uses: cachix/install-nix-action@V27
+        uses: cachix/install-nix-action@V31
         with:
-          nix_path: nixpkgs=channel:nixos-24.05
+          nix_path: nixpkgs=channel:nixos-25.05
       - name: Check flake
         run: nix flake check .?submodules=1#