fix: use fixture for self comparison test

Author: andrewkern

python/tests/test_tree_stats.py

@@ -2311,9 +2311,9 @@ def test_shapes(self, proportion):
 class TestBranchGeneticRelatedness(TestGeneticRelatedness, TopologyExamplesMixin):
     mode = "branch"
 
-    def test_single_sample_set_self_comparison(self):
+    def test_single_sample_set_self_comparison(self, ts_12_highrecomb_fixture):
         # Test for issue #3055 - self-comparisons with single sample set
-        ts = msprime.simulate(sample_size=10, Ne=10000, length=1000, random_seed=42)
+        ts = ts_12_highrecomb_fixture
         # Single sample set with self-comparison
         result = ts.genetic_relatedness([[0]], indexes=[(0, 0)], mode="branch")
         assert result.shape == (1,)