[1.7.x] Added 1.7.1 release notes for refs #23483.

* Fixed crash in ``contrib.sitemaps`` if ``lastmod`` returned a ``date`` rather

  than a ``datetime`` (:ticket:`23403`).

* Allowed migrations to work with ``app_label``\s that have the same last

  part (e.g. ``django.contrib.auth`` and ``vendor.auth``) (:ticket:`23483`).