character_subspace.m tests can be slow

[BenKBreen]

This combinations of discriminant d, weight k, and level n for the procedure testHeckeCharacterSubspace runs very slowly:

d = 65, k = [8, 8], n = 1, 2

[abhijit-mudigonda]

There also appears to be a low probability error now which I haven't seen before: https://github.com/edgarcosta/hilbertmodularforms/actions/runs/7228884583/job/19699007328?pr=423