This way nightly clippy warnings are not generated
when devshell is used.
Nighly Rust is also not cached, e.g. rust-analyzer has to be rebuilt
if version from fenix is used.
We update version in several .toml and .json files
on every release anyway, so updating pyproject.toml is easy.
setuptools_scm makes it more difficult to build
python packages for software distributions
because it requires full git checkout
with tags rather than just a worktree.
It is also possible to remove or move tags
after the release, so git revision no longer
pins python package version if setuptools_scm is used.
Compilation of vendored OpenSSL inside Nix is broken since
<https://github.com/alexcrichton/openssl-src-rs/pull/229> due to build
script changes.
There is anyway no need to compile vendored OpenSSL as nixpkgs already
contains OpenSSL package.
This fixes `nix build .#deltachat-rpc-server-x86_64-linux` and similar
commands which are used during releases.
