Format code with black

This commit fixes the style issues introduced in 50f37a0 according to the output
from black.

Details: https://deepsource.io/gh/MilesCranmer/PySR/transform/4ba37a50-24bf-4f71-8630-6a8794e45183/

pysr/sr.py

@@ -1176,7 +1176,6 @@ class PySRRegressor(BaseEstimator, RegressorMixin):
             nested_constraints_str += ")"
             nested_constraints = Main.eval(nested_constraints_str)
 
-
         if not already_ran:
             Main.eval("using Pkg")
             io = "devnull" if self.params["update_verbosity"] == 0 else "stderr"

test/test.py

@@ -174,7 +174,7 @@ class TestPipeline(unittest.TestCase):
             Xresampled=Xresampled,
             denoise=True,
             select_k_features=2,
-            nested_constraints={"/": {"+": 1, "-": 1}, "+": {"*": 4}}
+            nested_constraints={"/": {"+": 1, "-": 1}, "+": {"*": 4}},
         )
         model.fit(X, y)
         self.assertNotIn("unused_feature", model.latex())