Tests: avoid a race condition in grid/build_global_description_tree

In reference to #10073

diff --git a/tests/grid/build_global_description_tree.output b/tests/grid/build_global_description_tree.with_mpi=true.with_p4est=true.mpirun=1.output
similarity index 100%
rename from tests/grid/build_global_description_tree.output
rename to tests/grid/build_global_description_tree.with_mpi=true.with_p4est=true.mpirun=1.output