Fix Python docs build pre-commit failures.

[nikie]

Python docs build pre-commit is failing in all builds since 2021-10-26.

Pinning docutils to 0.17.1 version as a workaround, suggested in this Sphinx issue sphinx-doc/sphinx#9727 (comment).

---

Thank you for your contribution! Follow this checklist to help us incorporate your contribution quickly and easily:

• Choose reviewer(s) and mention them in a comment (R: @username).
• Format the pull request title like [BEAM-XXX] Fixes bug in ApproximateQuantiles, where you replace BEAM-XXX with the appropriate JIRA issue, if applicable. This will automatically link the pull request to the issue.
• Update CHANGES.md with noteworthy changes.
• If this contribution is large, please file an Apache Individual Contributor License Agreement.

See the Contributor Guide for more tips on how to make review process smoother.

ValidatesRunner compliance status (on master branch)

Lang	ULR	Dataflow	Flink	Samza	Spark	Twister2
Go	---					---
Java
Python	---					---
XLang						---

Examples testing status on various runners

Lang	ULR	Dataflow	Flink	Samza	Spark	Twister2
Go	---	---	---	---	---	---	---
Java	---		---	---	---	---	---
Python	---	---	---	---	---	---	---
XLang	---	---	---	---	---	---	---

Post-Commit SDK/Transform Integration Tests Status (on master branch)

Go	Java	Python

Pre-Commit Tests Status (on master branch)

---	Java	Python	Go	Website	Whitespace	Typescript
Non-portable
Portable	---			---	---	---

See .test-infra/jenkins/README for trigger phrase, status and link of all Jenkins jobs.

GitHub Actions Tests Status (on master branch)

See CI.md for more information about GitHub Actions CI.

[nikie]

R: @aaltay
Please take a look.
This seems to fix PythonLint ("Run PythonLint PreCommit") failures.

[codecov]

Codecov Report

Merging #15812 (9849940) into master (0b9fb71) will decrease coverage by 0.00%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #15812      +/-   ##
==========================================
- Coverage   83.55%   83.54%   -0.01%     
==========================================
  Files         445      445              
  Lines       61198    61198              
==========================================
- Hits        51135    51130       -5     
- Misses      10063    10068       +5     

Impacted Files	Coverage Δ
...hon/apache_beam/runners/direct/test_stream_impl.py	94.02% <0.00%> (-2.24%)	⬇️
...hon/apache_beam/runners/worker/bundle_processor.py	93.26% <0.00%> (-0.38%)	⬇️
...ks/python/apache_beam/runners/worker/sdk_worker.py	89.25% <0.00%> (-0.17%)	⬇️
sdks/python/apache_beam/runners/direct/executor.py	97.01% <0.00%> (+0.54%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 0b9fb71...9849940. Read the comment docs.

[nikie]

R: @tvalentyn

[tvalentyn]

Thank you!