Revert "chore(ci): switch to cache-nix-action for Nix store caching (#87)"

This reverts commit 0bbfd2d.

Author: ryoppippi

.github/actions/setup-nix/action.yaml

@@ -1,17 +1,18 @@
 name: "Setup Nix"
-description: "Install Nix and configure cache"
+description: "Install Nix and configure Cachix"
 runs:
   using: "composite"
   steps:
     - name: Install Nix
-      uses: cachix/install-nix-action@4e002c8ec80594ecd40e759629461e26c8abed15 # v31.9.0
+      uses: cachix/install-nix-action@0b0e072294b088b73964f1d72dfdac0951439dbd # v31.8.4
       with:
         github_access_token: ${{ github.token }}
 
-    - name: Cache Nix store
-      uses: nix-community/cache-nix-action@b426b118b6dc86d6952988d396aa7c6b09776d08 # v7
+    - name: Setup Cachix (numtide)
+      uses: cachix/cachix-action@0fc020193b5a1fa3ac4575aa3a7d3aa6a35435ad # v16
       with:
-        primary-key: nix-${{ runner.os }}
+        name: numtide
+        authToken: ""
 
     - name: Load Nix development environment
       shell: bash