Add entry for removal default value of request_context to changelog
ADD
changelog/1897.removal.rst
+Removed default value of ``None`` for the ``request_context`` parameter of ``urllib3.PoolManager.connection_from_pool_key``.
+
+This change should have no effect on users as the default value of ``None`` was an invalid option and was never used.

Add entry for removal default value of request_context to changelog

Co-authored-by: Seth Michael Larson <sethmichaellarson@gmail.com>