When outputting numbers of tests, align the text.

When outputting numbers of tests, align the text.

This then looks as follows:
-- Test category codim_one                  :    8 tests (and    0 test dependencies)
-- Test category distributed_grids          :  156 tests (and   28 test dependencies)
-- Test category feinterface                :    2 tests (and    0 test dependencies)
-- Test category fullydistributed_grids     :   80 tests (and   54 test dependencies)
-- Test category grid                       :  764 tests (and   54 test dependencies)
-- Test category mappings                   :    2 tests (and    0 test dependencies)
-- Test category matrix_free                :   52 tests (and   38 test dependencies)
-- Test category mpi                        :    8 tests (and    4 test dependencies)
-- Test category multigrid                  :  270 tests (and   79 test dependencies)
-- Test category multigrid-global-coarsening:   78 tests (and   50 test dependencies)
-- Test category sharedtria                 :    4 tests (and    4 test dependencies)
-- Test category simplex                    :   14 tests (and    0 test dependencies)