`io_uring_scheduler` can `throw` in `noexcept` functions causing termination

clang-tidy found these:

/home/eniebler/Code/stdexec/include/exec/linux/io_uring_context.hpp:528:14: warning: an exception may be thrown in function 'operator()' which should not throw exceptions [bugprone-exception-escape]
  528 |         void operator()() const noexcept {
      |              ^
/home/eniebler/Code/stdexec/include/exec/linux/io_uring_context.hpp:696:19: warning: an exception may be thrown in function 'tag_invoke' which should not throw exceptions [bugprone-exception-escape]
  696 |       friend void tag_invoke(stdexec::start_t, __io_task_facade& __self) noexcept {
      |                   ^

I notice there is another one in __stop_operation::__t::__start().