Builds failing with newer stdexec commits

[msimberg]

E.g.

/opt/spack/opt/spack/linux-ubuntu22.04-x86_64/gcc-11.4.0/stdexec-git.8bc7c7f06fe39831dea6852407ebe7f6be8fa9fd_main-y6gargi7ilhiqdh6as5iudd75lhwzzl2/include/stdexec/__detail/__transform_sender.hpp:179:58: error: exception specification of 'decltype(auto) stdexec::dependent_domain::transform_sender(_Sender&&, const _Env&) const [with _Sender = stdexec::__sexpr<<lambda closure object><lambda()>(), stdexec::{anonymous}::__anon>; _Env = stdexec::__env::env<>]' depends on itself

on https://gitlab.com/cscs-ci/ci-testing/webhook-ci/mirrors/4700071344751697/7514005670787789/-/jobs/7765210172/viewer.

GCC 11 stdexec pipelines will be disabled in #1180, and reenabled separately. Needs investigation if the issue is GCC 11 or the newer stdexec versions.