As 'python3' is scheduled to start pointing to that somewhere in June.
The dependency on 'sip' was changed to 08a26e4579
out of caution, but it seems to work fine with the new default sip.
This avoids picking up libraries from the users' PYTHONPATH, which
might conflict with the libraries that inkcut actually expects to
run with.
You can reproduce that problem with `nix-shell -p inkcut python310Packages.atom --run inkcut`:
it will pick up the python 3.10 atom while inkcut is still built with pyton 3.9,
leading to an error on startup.
Fixes#159179
