[docs] Added changelog entry for v0.21.2.

Signed-off-by: Michael Seifert <[email protected]>

Author: seifertm

docs/source/reference/changelog.rst

@@ -84,6 +84,10 @@ This release has been yanked from PyPI due to fundamental issues with the _async
 - Remove support for Python 3.7
 - Declare support for Python 3.12
 
+0.21.2 (2024-04-29)
+===================
+- Fix compatibility with pytest 8.2. Backport of `#800 <https://github.com/pytest-dev/pytest-asyncio/pull/800>`_ to pytest-asyncio v0.21 for users who are unable to upgrade to a more recent version (see `#706`_)
+
 0.21.1 (2023-07-12)
 ===================
 - Output a proper error message when an invalid ``asyncio_mode`` is selected.