test: Fix exclude_lines for coverage

`exclude_lines` was only considering TYPE_CHECKING if it was preceded
with at least one space.

setup.cfg

@@ -39,7 +39,7 @@ exclude_lines =
     pragma: no cover
 
     # TYPE_CHECKING guarded code only affects type checkers.
-    ^ +if (False|TYPE_CHECKING):
+    ^ *if (False|TYPE_CHECKING):
     # constant used in protocols and abstract methods, does not run anything
     # and has no side effects.
     ^ +\.\.\.$