Cause: upstream nodejs build failure (same as #1717)

Test NixOS fails in both test-home-manager-builds jobs (yanosea@yanoNixOs, yanosea@yanoNixOsWsl) while building nodejs-slim:

error: Cannot build '/nix/store/njhj371sv6q9b1h2lwxj49gf8yckyb6f-nodejs-slim-26.9.0.drv'.
       Reason: builder failed with exit code 2.
> Failed tests:
> out/Release/node /build/node-v26.9.0/test/parallel/test-fs-cp-async-file-modes.mjs
> make: *** [Makefile:631: test-ci-js] Error 1

test-fs-cp-async-file-modes.mjs calls chmodSync and hits EPERM: operation not permitted inside the Nix build sandbox, so the check phase aborts. nodejs-slim is pulled in through home-manager-path, which is why only the home-manager jobs fail while test-nixos-builds succeeds.

Why this is upstream

• The failing derivation is njhj371sv6q9b1h2lwxj49gf8yckyb6f-nodejs-slim-26.9.0.drv — the exact same store hash that failed on ⚡deps(nix): update dependencies in flake.lock (2026-09-19) #1717 yesterday. Hydra fails on the same derivation, so there is no binary cache entry and CI has to build it from source.
• Tracked upstream at Build failure: nodejs-slim_26.x86_64-linux NixOS/nixpkgs#564449 (still open).
• The fix is test: avoid call to chmodSync in test-fs-cp-async-file-modes nodejs/node#66104, which makes the test skip chmodSync. It is still open and unmerged, and no nixpkgs PR carries a backport yet.

This PR bumps nixpkgs b1b87598 → e554fab7, the same revision #1717 tried, so the outcome is unchanged. Test Lint and Test Darwin both passed.

Action

Closing without a local patch, per the usual policy for upstream breakage — no overlay, no pin. Once nodejs/node#66104 lands and reaches nixpkgs-unstable, a later daily auto-update will pick it up and pass on its own.