message: Use GlobalMPISession in the test_sedov unit test
diff: #include "mfem.hpp"
  #include "general/forall.hpp"
  +extern mfem::MPI_Session *GlobalMPISession;
  +
  #ifdef MFEM_USE_MPI
  #define PFesGetParMeshGetComm(pfes) pfes.GetParMesh()->GetComm()
  #define PFesGetParMeshGetComm0(pfes) pfes.GetParMesh()->GetComm()
  @@ -3672,7 +3674,7 @@ static void sedov_tests(MPI_Session &mpi)
  TEST_CASE("Sedov", "[Sedov]")
  {
  - MPI_Session mpi;
  + MPI_Session &mpi = *GlobalMPISession;
  sedov_tests(mpi);
  }
  @@ -3680,7 +3682,7 @@ TEST_CASE("Sedov", "[Sedov]")
  TEST_CASE("Sedov", "[Sedov]")
  {
  - MPI_Session mpi;
  + MPI_Session &mpi = *GlobalMPISession;
  Device device;
  device.Configure(MFEM_SEDOV_DEVICE);
  if (mpi.Root()) {device.Print();}
  