Update sphinx requirement from <7.5 to <8.1 (#791)

* Update sphinx requirement from <7.5 to <8.1

Updates the requirements on [sphinx](https://github.com/sphinx-doc/sphinx) to permit the latest version.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/v8.0.2/CHANGES.rst)
- [Commits](https://github.com/sphinx-doc/sphinx/compare/v0.1.61611...v8.0.2)

---
updated-dependencies:
- dependency-name: sphinx
  dependency-type: direct:development
...

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* Update changelog

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---------

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Co-authored-by: dependabot[bot] <dependabot[bot]@users.noreply.github.com>

CHANGELOG.md

@@ -17,7 +17,7 @@ Inspired from [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 ### Security
 ### Dependencies
 - Bump `pytest-asyncio` from <=0.23.7 to <=0.23.8 ([#787](https://github.com/opensearch-project/opensearch-py/pull/787))
-- Bump `sphinx` from <7.4 to <7.5 ([#788](https://github.com/opensearch-project/opensearch-py/pull/788))
+- Bump `sphinx` from <7.4 to <8.1 ([#788](https://github.com/opensearch-project/opensearch-py/pull/788), [#791](https://github.com/opensearch-project/opensearch-py/pull/791))
 - Bump `urllib3` from >=1.26.18 to >=1.26.19 ([#793](https://github.com/opensearch-project/opensearch-py/pull/793))
 - Bump `requests` from >=2.4.0 to >=2.32.0 ([#793](https://github.com/opensearch-project/opensearch-py/pull/793))
 - Bump `certifi` from >=2022.12.07 to >=2024.07.04 ([#793](https://github.com/opensearch-project/opensearch-py/pull/793))