flake.lock: Update

Flake lock file updates:

• Updated input 'fenix':
    'github:nix-community/fenix/aaeaf4574767a0f5ed1787e990139aefcf4db103?narHash=sha256-iGb6ptUaNBOCftKnNJiWT5z1ftngfNtwqJkD8Z9Vwfw%3D' (2024-03-30)
  → 'github:nix-community/fenix/a4b7a4acfb44ee78785b0b53667066a9b1e32245?narHash=sha256-FJJMYOmzST4gOiOo4g5XicKKALv8SWqqk2kntpIF3NM%3D' (2024-05-18)
• Updated input 'fenix/rust-analyzer-src':
    'github:rust-lang/rust-analyzer/f5a9250147f6569d8d89334dc9cca79c0322729f?narHash=sha256-dyezzeSbWMpflma%2BE9USmvSxuLgGcNGcGw3cOnX36ko%3D' (2024-03-29)
  → 'github:rust-lang/rust-analyzer/83ba42043166948db91fcfcfe30e0b7eac10b3d5?narHash=sha256-EyjtjocGLtB7tqyqwBfadP4y5BBtT5EkoG3kq/zym5U%3D' (2024-05-16)
• Updated input 'nixpkgs':
    'github:nixos/nixpkgs/d8fe5e6c92d0d190646fb9f1056741a229980089?narHash=sha256-iMUFArF0WCatKK6RzfUJknjem0H9m4KgorO/p3Dopkk%3D' (2024-03-29)
  → 'github:nixos/nixpkgs/4a6b83b05df1a8bd7d99095ec4b4d271f2956b64?narHash=sha256-%2BNpbZRCRisUHKQJZF3CT%2Bxn14ZZQO%2BKjxIIanH3Pvn4%3D' (2024-05-17)
• Updated input 'rust-overlay':
    'github:oxalica/rust-overlay/7cf3d11d06dcd12fb62ca2c039f3c5e25b53c5a7?narHash=sha256-I2/x/jFd7MAuIi3%2BkncIF0zJwhkFzxpi5XFdT2RLOF8%3D' (2024-03-30)
  → 'github:oxalica/rust-overlay/4731829dec4859921bfc0e1548478207d6c9c8fa?narHash=sha256-krjs9VkDoRrYNQVyCTXUGUfAJziCk0Fkki1ZnnmNgjk%3D' (2024-05-18)