Format code with black

This commit fixes the style issues introduced in 3c6a750 according to the output
from black.

Details: https://deepsource.io/gh/MilesCranmer/PySR/transform/e884243d-a351-4ff3-be0e-5c4f0e3d0980/

pysr/sr.py

@@ -15,7 +15,7 @@ from multiprocessing import cpu_count
 is_julia_warning_silenced = False
 
 
-def install(julia_project=None): # pragma: no cover
+def install(julia_project=None):  # pragma: no cover
     import julia
 
     julia.install()