Third-party stubs: import from collections.abc where possible (#7637)

stubs/chevron/chevron/renderer.pyi

@@ -1,5 +1,6 @@
 from _typeshed import StrPath, SupportsRead
-from typing import Any, MutableSequence, Sequence
+from collections.abc import MutableSequence, Sequence
+from typing import Any
 
 g_token_cache: dict[str, list[tuple[str, str]]]  # undocumented
 

stubs/chevron/chevron/tokenizer.pyi

@@ -1,4 +1,4 @@
-from typing import Iterator
+from collections.abc import Iterator
 
 class ChevronError(SyntaxError): ...