Update cachix/install-nix-action digest to 13d8dd5

Author: renovate[bot]

.github/workflows/ci.yml

@@ -97,7 +97,7 @@ jobs:
         uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
 
       - name: Install Nix
-        uses: cachix/install-nix-action@630ae543ea3a38a9a4166f03376c02c50f408342 # v31
+        uses: cachix/install-nix-action@13d8dd58da0234aa297dedd986986ccb8e7f3e24 # v31
         with:
           nix_path: nixpkgs=channel:nixpkgs-26.05-darwin