build: bump azure-search-documents from 11.4.0b6 to 11.6.0b8

Bumps [azure-search-documents](https://github.com/Azure/azure-sdk-for-python) from 11.4.0b6 to 11.6.0b8.
- [Release notes](https://github.com/Azure/azure-sdk-for-python/releases)
- [Changelog](https://github.com/Azure/azure-sdk-for-python/blob/main/sdk/search/azure-search-documents/CHANGELOG.md)
- [Commits](Azure/azure-sdk-for-python@azure-search-documents_11.4.0b6...azure-search-documents_11.6.0b8)

---
updated-dependencies:
- dependency-name: azure-search-documents
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

requirements.txt

@@ -1,7 +1,7 @@
 azure-identity==1.17.1
 # Flask[async]==2.3.2
 openai==1.6.1
-azure-search-documents==11.4.0b6
+azure-search-documents==11.6.0b8
 azure-storage-blob==12.24.0
 python-dotenv==1.0.0
 azure-cosmos==4.9.0