Disable more MPI tests that use sync_wait.

libs/core/async_mpi/tests/unit/mpi_ring_async_executor.cpp

@@ -172,6 +172,7 @@ int hpx_main(hpx::program_options::variables_map& vm)
 // will execute hpx_main on an hpx thread
 int main(int argc, char* argv[])
 {
+#if !defined(HPX_HAVE_STDEXEC)
     // if this test is run with distributed runtime, we need to make sure
     // that all ranks run their main function
     std::vector<std::string> cfg = {"hpx.run_hpx_main!=1"};
@@ -208,4 +209,5 @@ int main(int argc, char* argv[])
     MPI_Finalize();
 
     return result || hpx::util::report_errors();
+#endif
 }