chore(deps): update determinatesystems/nix-installer-action action to v20

Author: renovate[bot]

.github/workflows/update-flake.yml

@@ -17,7 +17,7 @@ jobs:
         with:
           persist-credentials: false
       - name: Install Nix
-        uses: DeterminateSystems/nix-installer-action@v19
+        uses: DeterminateSystems/nix-installer-action@v20
       - name: Update flake.lock
         id: update
         uses: DeterminateSystems/update-flake-lock@v27