ci(tools): update cachix/install-nix-action digest to 7ab6e7f (#89)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

.github/workflows/flake.yml

@@ -32,7 +32,7 @@ jobs:
           token: ${{ steps.token.outputs.token }}
 
       - name: Install nix
-        uses: cachix/install-nix-action@9280e7aca88deada44c930f1e2c78e21c3ae3edd # v31
+        uses: cachix/install-nix-action@7ab6e7fd29da88e74b1e314a4ae9ac6b5cda3801 # v31
 
       - name: Update flake
         run: nix flake update