Update cachix/install-nix-action action to v31

Author: renovate[bot]

.github/workflows/workflow.yaml

@@ -32,7 +32,7 @@ jobs:
         with:
           path: ~/repo-cache
           key: repo-cache-${{ runner.os }}-nixpkgs-${{ env.cache-version }}
-      - uses: cachix/install-nix-action@v30
+      - uses: cachix/install-nix-action@v31
         with:
           nix_path: nixpkgs=./nixpkgs.nix
       - uses: tweag/configure-bazel-remote-cache-auth@v0