flake.lock: Update
Flake lock file updates:
• Updated input 'nixvim':
'github:nix-community/nixvim/03a638205b5cb04ba9c2ed6c604e137b15f07fa1?narHash=sha256-I7ymDe6UQooHy9I9wrafKCCDnRbox/EMWAgJgpm7fGs%3D' (2026-01-15)
→ 'github:nix-community/nixvim/5b138edcb2f1c3ed4b29eca3658f04f0639b98b3?narHash=sha256-YRU0IHMzXluZxr0JDfq9jtblb4DV7MIB5wj2jYMFKQc%3D' (2026-01-20)