fix(ci): switch to DeterminateSystems/nix-installer-action

The cachix/install-nix-action@v27 fails on macOS runners due to
existing _nixbld users (eDSRecordAlreadyExists error). The Determinate
Systems installer handles this gracefully.

Author: subtleGradient

.github/workflows/zig-tests.yaml

@@ -37,9 +37,7 @@ jobs:
       - uses: actions/checkout@v4
 
       - name: Install Nix
-        uses: cachix/install-nix-action@v27
-        with:
-          nix_path: nixpkgs=channel:nixos-unstable
+        uses: DeterminateSystems/nix-installer-action@main
 
       - name: Cache Zig
         uses: actions/cache@v4
@@ -86,9 +84,7 @@ jobs:
       - uses: actions/checkout@v4
 
       - name: Install Nix
-        uses: cachix/install-nix-action@v27
-        with:
-          nix_path: nixpkgs=channel:nixos-unstable
+        uses: DeterminateSystems/nix-installer-action@main
 
       - name: Cache Zig
         uses: actions/cache@v4
@@ -118,9 +114,7 @@ jobs:
       - uses: actions/checkout@v4
 
       - name: Install Nix
-        uses: cachix/install-nix-action@v27
-        with:
-          nix_path: nixpkgs=channel:nixos-unstable
+        uses: DeterminateSystems/nix-installer-action@main
 
       - name: Cache Zig
         uses: actions/cache@v4
@@ -147,9 +141,7 @@ jobs:
       - uses: actions/checkout@v4
 
       - name: Install Nix
-        uses: cachix/install-nix-action@v27
-        with:
-          nix_path: nixpkgs=channel:nixos-unstable
+        uses: DeterminateSystems/nix-installer-action@main
 
       - name: Cache Zig
         uses: actions/cache@v4
@@ -241,9 +233,7 @@ jobs:
       - uses: actions/checkout@v4
 
       - name: Install Nix
-        uses: cachix/install-nix-action@v27
-        with:
-          nix_path: nixpkgs=channel:nixos-unstable
+        uses: DeterminateSystems/nix-installer-action@main
 
       - name: Cache Zig
         uses: actions/cache@v4
@@ -292,9 +282,7 @@ jobs:
       - uses: actions/checkout@v4
 
       - name: Install Nix
-        uses: cachix/install-nix-action@v27
-        with:
-          nix_path: nixpkgs=channel:nixos-unstable
+        uses: DeterminateSystems/nix-installer-action@main
 
       - name: Setup Node.js
         uses: actions/setup-node@v4