ci(github-action): pin action determinatesystems/nix-installer-action to ef8a148

Author: renovate[bot]

.github/workflows/ci.yml

@@ -14,7 +14,7 @@ jobs:
         with:
           go-version: 1.25
       - name: Install Nix
-        uses: DeterminateSystems/nix-installer-action@main
+        uses: DeterminateSystems/nix-installer-action@ef8a148080ab6020fd15196c2084a2eea5ff2d25 # main
       - name: Nix build (flake default)
         run: nix build .#default
       - name: Test