Mark stub-only private symbols as @type_check_only in third-party stubs (#14545)

stubs/defusedxml/defusedxml/lxml.pyi

@@ -1,6 +1,6 @@
 import threading
 from _typeshed import Incomplete
-from typing import Final, Literal
+from typing import Final, Literal, type_check_only
 
 # Not bothering with types here as lxml support is supposed to be dropped in a future version of defusedxml
 
@@ -24,6 +24,7 @@ def tostring(
 ): ...
 
 # Should be imported from lxml.etree.ElementBase, but lxml lacks types
+@type_check_only
 class _ElementBase: ...
 
 class RestrictedElement(_ElementBase):

stubs/defusedxml/defusedxml/xmlrpc.pyi

@@ -1,9 +1,9 @@
 import gzip
 from _typeshed import ReadableBuffer
-from typing import Final, Protocol, runtime_checkable
+from typing import Final, Protocol, type_check_only
 from xmlrpc.client import ExpatParser, Unmarshaller
 
-@runtime_checkable
+@type_check_only
 class _Readable(Protocol):
     def read(self, size: int | None = -1) -> bytes: ...