CI(deps): Replace nix install action with DeterminateSystems/determinate-nix-action v3.8.2 (OSGeo#6073)

Author: renovate[bot]

.github/workflows/test-nix.yml

@@ -31,7 +31,7 @@ jobs:
       - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
 
       - name: Install nix
-        uses: DeterminateSystems/nix-installer-action@c723f3a885e3f1d866d91f4f0c33dd44b1fc7c60 # v18
+        uses: DeterminateSystems/determinate-nix-action@2b7bca919ce8854111c6f9135091ddf5eea8e0eb # v3.8.2
 
       - name: Setup cachix
         uses: cachix/cachix-action@0fc020193b5a1fa3ac4575aa3a7d3aa6a35435ad # v16