flake.lock: Update (#859)

Flake lock file updates:

• Updated input 'neovim-nightly':
    'github:nix-community/neovim-nightly-overlay/b550599eedc54514f5b71cee8e480e337d104d84?narHash=sha256-Asr6gDwzxvcglRaXEZSTL4lEA6braemURJc6wKBhKrs%3D' (2026-03-13)
  → 'github:nix-community/neovim-nightly-overlay/49ff0692b00466bee56c3c72e91e4d0b8342a93b?narHash=sha256-IBAHAaYfiR9fhR%2By6ZUdM697dht26tvrWeIrTLwBs3E%3D' (2026-03-14)
• Updated input 'neovim-nightly/neovim-src':
    'github:neovim/neovim/957eb1fde04496b4a2c07fd8427a8d78844d1bf7?narHash=sha256-vWu0zLThxpsx6vbPK5eAgvkMKu1LV8tbybS/sjWn8S8%3D' (2026-03-12)
  → 'github:neovim/neovim/fd1e019e90e76bb3f6236210ac6287f3b8d4d47f?narHash=sha256-Oj4HMwF261bJCS/zqgmqdxoCBSeEjwghxW%2B1MA9Ktik%3D' (2026-03-13)
• Updated input 'neovim-nightly/nixpkgs':
    'github:NixOS/nixpkgs/b6067cc0127d4db9c26c79e4de0513e58d0c40c9?narHash=sha256-NXrKzNMniu4Oam2kAFvqJ3GB2kAvlAFIriTAheaY8hw%3D' (2026-03-11)
  → 'github:NixOS/nixpkgs/75690239f08f885ca9b0267580101f60d10fbe62?narHash=sha256-Xy3WEpUAbpsz8ydgvVAQAGGB/WB%2B8cNA5cshiL0McTI%3D' (2026-03-11)
• Updated input 'nixpkgs':
    'github:nixos/nixpkgs/b6067cc0127d4db9c26c79e4de0513e58d0c40c9?narHash=sha256-NXrKzNMniu4Oam2kAFvqJ3GB2kAvlAFIriTAheaY8hw%3D' (2026-03-11)
  → 'github:nixos/nixpkgs/75690239f08f885ca9b0267580101f60d10fbe62?narHash=sha256-Xy3WEpUAbpsz8ydgvVAQAGGB/WB%2B8cNA5cshiL0McTI%3D' (2026-03-11)

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

Author: mrcjkb