Enable msprime tests on OSX

Author: jeromekelleher

tests/test_simulated_data.py

@@ -1,5 +1,4 @@
-import sys
-
+import msprime
 import numpy.testing as nt
 import pysam
 import pytest
@@ -8,13 +7,9 @@
 from bio2zarr import vcf2zarr
 
 
-@pytest.mark.skipif(sys.platform == "darwin", reason="msprime OSX pip packages broken")
 class TestTskitRoundTripVcf:
     @pytest.mark.parametrize("ploidy", [1, 2, 3, 4])
     def test_ploidy(self, ploidy, tmp_path):
-        # FIXME importing here so pytest.skip avoids importing msprime.
-        import msprime
-
         ts = msprime.sim_ancestry(
             2,
             population_size=10**4,