flake: Update nixpkgs

• Updated input 'nixpkgs':
    'github:NixOS/nixpkgs/cd32a774ac52caaa03bcfc9e7591ac8c18617ced?narHash=sha256-VtMQg02B3kt1oejwwrGn50U9Xbjgzfbb5TV5Wtx8dKI%3D' (2025-08-17)
  → 'github:NixOS/nixpkgs/d98ce345cdab58477ca61855540999c86577d19d?narHash=sha256-O2CIn7HjZwEGqBrwu9EU76zlmA5dbmna7jL1XUmAId8%3D' (2025-08-26)

This update contains d1266642a8722f2a05e311fa151c1413d2b9653c, which
is necessary for the TOML timestamps to get tested via nixpkgsLibTests job.

(cherry picked from commit 625477a)

Author: xokdvium