Temporarily limit the number of ranks for L2TriToQuad tests

Author: nmnobre

test/tests/mfem/transfers/l2_libmesh_parent_mfem_sub/tests

@@ -38,6 +38,7 @@
       cli_args = 'Mesh/file=../../mesh/square_quad9.e '
                 'Outputs/file_base=libmesh_parent_scalar_mfem_sub_tri_to_quad '
                 'mfem_app0:Mesh/file=../../mesh/square_tri6.e '
+      max_parallel = 6 # under investigation
     []
     [L2Hex]
       type = CSVDiff

test/tests/mfem/transfers/l2_mfem_parent_libmesh_sub/tests

@@ -38,6 +38,7 @@
       cli_args = 'Mesh/file=../../mesh/square_quad9.e '
                 'Outputs/file_base=mfem_parent_libmesh_sub_scalar_tri_to_quad '
                 'libmesh_app0:Mesh/file=../../mesh/square_tri6.e '
+      max_parallel = 15 # under investigation
     []
     [L2Hex]
       type = CSVDiff