nix/default: disable version check

[khaneliman]

Downstream added version check, causes this flake to fail building.

With latest nixpkgs:

 > Executing versionCheckPhase
       > Did not find version 0.12.0+date=2025-03-06_dirty in the output of the command /nix/store/zpb7x04yv9d1z2mrm5wml644v4kgfr6k-waybar-0.12.0+date=2025-03-06_dirty/bin/waybar --version
       > env: '--version': No such file or directory

[mslxl]

It should close #3957

[khaneliman]

@Alexays whenever you get a chance