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

stubs/python-slugify/slugify/slugify.pyi

@@ -1,4 +1,4 @@
-from typing import Iterable
+from collections.abc import Iterable
 
 def smart_truncate(
     string: str, max_length: int = ..., word_boundary: bool = ..., separator: str = ..., save_order: bool = ...

stubs/python-slugify/slugify/special.pyi

@@ -1,4 +1,4 @@
-from typing import Sequence
+from collections.abc import Sequence
 
 def add_uppercase_char(char_list: Sequence[tuple[str, str]]) -> Sequence[tuple[str, str]]: ...