It does the necessary overrides for stopping doc builds and excluding certain
inputs and outputs. We can't just set `dontBuildDocs` in the derivation
because that's not a setting recognized by the Nixpkgs Python build system.
It was already computed for the derivation we're going to override. It won't
be recomputed again as a result of `overrideAttrs` so we recompute it and
include it in the override.
