Without the change the build fails on `master` as
https://hydra.nixos.org/build/247694706:
In file included from /build/source/external/VSRTL/interface/vsrtl_vcdfile.cpp:1:
/build/source/external/VSRTL/interface/vsrtl_vcdfile.h:31:20: error: 'uint64_t' has not been declared
31 | void writeTime(uint64_t time);
| ^~~~~~~~
As the fix was done in one of the external modules it seemed easier to
pull unstable `master` version. Switched to `qt6` and checked if it
starts.
c218341c52