Fix typos discovered by codespell

[cclauss]

Fix typos discovered by codespell - https://pypi.org/project/codespell

% codespell

./docs/reference/changelog.rst:9: changlog ==> changelog
./pytest_asyncio/plugin.py:491: inteded ==> intended

% codespell --write-changes

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.64%. Comparing base (7a69596) to head (a879946).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1296   +/-   ##
=======================================
  Coverage   93.64%   93.64%           
=======================================
  Files           2        2           
  Lines         409      409           
  Branches       44       44           
=======================================
  Hits          383      383           
  Misses         20       20           
  Partials        6        6           

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