Format code with black

This commit fixes the style issues introduced in a190947 according to the output
from black.

Details: https://deepsource.io/gh/MilesCranmer/PySR/transform/f088c279-f5ed-4ac1-9fd9-aad0d03da1fe/

test/test.py

@@ -217,7 +217,7 @@ class TestPipeline(unittest.TestCase):
         model = PySRRegressor(
             unary_operators=["cos"],
             select_k_features=3,
-            early_stop_condition=1e-4, # Stop once most accurate equation is <1e-4 MSE
+            early_stop_condition=1e-4,  # Stop once most accurate equation is <1e-4 MSE
             Xresampled=Xresampled,
             maxsize=12,
             **self.default_test_kwargs,