Fix typo picked up by codespell

Author: JohnGarbutt

tox.ini

@@ -26,7 +26,7 @@ commands =
 
 [testenv:black]
 # TODO: understand why ruff doesn't fix
-# line lenghts as well as black does
+# line lengths as well as black does
 commands = black {tox_root} --check
 
 [testenv:codespell]