Make protocol arguments positional only as suggested in the review

Author: abravalheri

stdlib/_typeshed/importlib.pyi

@@ -15,4 +15,4 @@ class MetaPathFinderProtocol(Protocol):
     def find_spec(self, fullname: str, path: Sequence[str] | None, target: ModuleType | None = ..., /) -> ModuleSpec | None: ...
 
 class PathEntryFinderProtocol(Protocol):
-    def find_spec(self, fullname: str, target: ModuleType | None = ...) -> ModuleSpec | None: ...
+    def find_spec(self, fullname: str, target: ModuleType | None = ..., /) -> ModuleSpec | None: ...