Merge pull request open-mpi#12898 from hppritcha/add_a_return_val_to_sessions_test

examples: add return 0 to sessions smoke test

Author: hppritcha

examples/hello_sessions_c.c

@@ -17,4 +17,5 @@ int main(int argc, char** argv) {
   MPI_Session_init(MPI_INFO_NULL, MPI_ERRORS_RETURN, &s2);
   MPI_Session_finalize(&s2);
   MPI_Info_free(&info);
+  return 0;
 }