Re-enable tor unit tests on apple-darwin

[fmarier]

As of tor 0.4.18.18, these tests are failing on macOS (arm64):

FAIL: src/test/unittest_part8.sh

util/monotonic_time_add_msec: 
  FAIL src/test/test_util.c:6644: assert(monotime_coarse_diff_msec32_(&ct1, &ct2) OP_GT 1323): 1310 vs 1323
  [monotonic_time_add_msec FAILED]

[mihaiplesa]

Is this still the case?

[fmarier]

They are now also disabled on x86_64-apple-darwin: #166