Fixes documentation link test

[nezhar]

The test-docs workflow added with #6967 needs to be reverted to Python 3.9, otherwiese the docs cannot be served. This might be related to the version of mkdocs that is currently in use.

Run mkdocs serve & Traceback (most recent call last): File "/opt/hostedtoolcache/Python/3.10.[12](https://github.com/nezhar/django-rest-framework/actions/runs/5888078513/job/15968572627#step:5:13)/x64/bin/mkdocs", line 5, in <module> from mkdocs.__main__ import cli File "/opt/hostedtoolcache/Python/3.10.12/x64/lib/python3.10/site-packages/mkdocs/__main__.py", line 16, in <module> from mkdocs import config # noqa: E402 File "/opt/hostedtoolcache/Python/3.10.12/x64/lib/python3.10/site-packages/mkdocs/config/__init__.py", line 2, in <module> from mkdocs.config.defaults import DEFAULT_SCHEMA File "/opt/hostedtoolcache/Python/3.10.12/x64/lib/python3.10/site-packages/mkdocs/config/defaults.py", line 1, in <module> from mkdocs.config import config_options File "/opt/hostedtoolcache/Python/3.10.12/x64/lib/python3.10/site-packages/mkdocs/config/config_options.py", line 2, in <module> from collections import Sequence, namedtuple ImportError: cannot import name 'Sequence' from 'collections' (/opt/hostedtoolcache/Python/3.10.12/x64/lib/python3.10/collections/__init__.py) 

[nezhar]

The current run will produce an output that can be used for further fixes in the docs: https://github.com/encode/django-rest-framework/actions/runs/5888144582/job/15968764328#step:8:194

ERROR Crawled 133 urls with 13 error(s) in 4.18 seconds Start URL(s): http://localhost:8000/ not found (404): http://localhost:8000/api-guide/schemas/openapi-operationid from http://localhost:8000/api-guide/schemas/ from http://localhost:8000/api-guide/schemas/#examples not found (404): http://localhost:8000/community/topics/third-party-packages/#existing-third-party-packages from http://localhost:8000/community/third-party-packages/ not found (404): http://localhost:8000/community/api-guide/schemas/#schemas-as-documentation from http://localhost:8000/community/3.5-announcement/ not found (404): http://localhost:8000/community/api-guide/schemas/#the-get_schema_view-shortcut from http://localhost:8000/community/3.5-announcement/ not found (404): http://localhost:8000/community/api-guide/schemas/#schemagenerator from http://localhost:8000/community/3.5-announcement/ not found (404): http://localhost:8000/community/3.4-announcement/api-clients#command-line-client from http://localhost:8000/community/3.4-announcement/ not found (404): http://localhost:8000/community/3.4-announcement/api-clients#python-client-library from http://localhost:8000/community/3.4-announcement/ not found (404): http://localhost:8000/community/tutorial/7-schemas-and-client-libraries/ from http://localhost:8000/community/3.4-announcement/ not found (404): http://localhost:8000/community/api-guide/schemas/ from http://localhost:8000/community/3.4-announcement/ not found (404): http://localhost:8000/community/api-guide/metadata/#custom-metadata-classes from http://localhost:8000/community/3.4-announcement/ not found (404): http://localhost:8000/community/3.4-announcement/release-notes#34 from http://localhost:8000/community/3.4-announcement/ not found (404): http://localhost:8000/community/api-guide/fields#jsonfield from http://localhost:8000/community/3.3-announcement/ not found (404): http://localhost:8000/community/api-guide/pagination/#custom-pagination-styles from http://localhost:8000/community/3.1-announcement/ Error: Process completed with exit code 1.