CI(deps): Update DeterminateSystems/determinate-nix-action action to v3.9.1 (OSGeo#6283)

Author: renovate[bot]

.github/workflows/test-nix.yml

@@ -31,7 +31,7 @@ jobs:
       - uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
 
       - name: Install nix
-        uses: DeterminateSystems/determinate-nix-action@b7303d63f88908d15f0bcb207e60b3a0ea7f1712 # v3.8.6
+        uses: DeterminateSystems/determinate-nix-action@fd3eb131b9b46cc1dd978a7c0ba3fce79dd7d3eb # v3.9.1
 
       - name: Setup cachix
         uses: cachix/cachix-action@0fc020193b5a1fa3ac4575aa3a7d3aa6a35435ad # v16