chore: Make nix hook optional (#6431)

This change makes the `nix` pre-commit hook optional in development environments, and enforced only inside Github Actions.

.github/workflows/pre-commit.yml

@@ -11,7 +11,7 @@ on:
 jobs:
   # Call the workflow in the XRPLF/actions repo that runs the pre-commit hooks.
   run-hooks:
-    uses: XRPLF/actions/.github/workflows/pre-commit.yml@320be44621ca2a080f05aeb15817c44b84518108
+    uses: XRPLF/actions/.github/workflows/pre-commit.yml@56de1bdf19639e009639a50b8d17c28ca954f267
     with:
       runs_on: ubuntu-latest
       container: '{ "image": "ghcr.io/xrplf/ci/tools-rippled-pre-commit:sha-41ec7c1" }'

.pre-commit-config.yaml

@@ -61,7 +61,15 @@ repos:
     hooks:
       - id: nix-fmt
         name: Format Nix files
-        entry: nix --extra-experimental-features 'nix-command flakes' fmt
+        entry: |
+          bash -c '
+            if command -v nix &> /dev/null || [ "$GITHUB_ACTIONS" = "true" ]; then
+              nix --extra-experimental-features "nix-command flakes" fmt "$@"
+            else
+              echo "Skipping nix-fmt: nix not installed and not in GitHub Actions"
+              exit 0
+            fi
+          ' --
         language: system
         types:
           - nix