[PR #5774/87e4f3b2 backport][3.8] Enable Nitpicky mode in Sphinx docs

[patchback]

This is a backport of PR #5774 as merged into master (87e4f3b).

What do these changes do?

Make sphinx strict about any warnings.

Are there changes in behavior for the user?

No

Related issue number

Resolves #5518

Checklist

• I think the code is well written
• Unit tests for the changes exist
• Documentation reflects the changes
• If you provide code modification, please add yourself to CONTRIBUTORS.txt
  • The format is <Name> <Surname>.
  • Please keep alphabetical order, the file is sorted by names.
• Add a new news fragment into the CHANGES folder
  • name it <issue_id>.<type> for example (588.bugfix)
  • if you don't have an issue_id change it to the pr id after creating the pr
  • ensure type is one of the following:
    • .feature: Signifying a new feature.
    • .bugfix: Signifying a bug fix.
    • .doc: Signifying a documentation improvement.
    • .removal: Signifying a deprecation or removal of public API.
    • .misc: A ticket has been closed, but it is not of interest to users.
  • Make sure to use full sentences with correct case and punctuation, for example: "Fix issue with non-ascii contents in doctest text files."

[codecov]

Codecov Report

Merging #5775 (87e4f3b) into 3.8 (8ce3013) will decrease coverage by 0.35%.
The diff coverage is 97.04%.

❗ Current head 87e4f3b differs from pull request most recent head 4d2481b. Consider uploading reports for the commit 4d2481b to get more accurate results

@@            Coverage Diff             @@
##              3.8    #5775      +/-   ##
==========================================
- Coverage   97.53%   97.17%   -0.36%     
==========================================
  Files          44       41       -3     
  Lines        8844     8865      +21     
  Branches     1424     1425       +1     
==========================================
- Hits         8626     8615      -11     
- Misses        102      133      +31     
- Partials      116      117       +1     

Flag	Coverage Δ
unit	97.06% <96.78%> (-0.31%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
aiohttp/web_protocol.py	86.41% <ø> (-4.20%)	⬇️
aiohttp/web_request.py	95.99% <ø> (-1.57%)	⬇️
aiohttp/web_response.py	98.21% <ø> (-0.06%)	⬇️
aiohttp/web_routedef.py	98.13% <ø> (+0.03%)	⬆️
aiohttp/web_runner.py	97.74% <ø> (+0.11%)	⬆️
aiohttp/web_server.py	94.28% <ø> (-5.72%)	⬇️
aiohttp/web_urldispatcher.py	97.83% <ø> (+0.23%)	⬆️
aiohttp/worker.py	94.91% <ø> (-1.81%)	⬇️
aiohttp/locks.py	92.85% <66.66%> (ø)
aiohttp/resolver.py	93.33% <81.25%> (-1.83%)	⬇️
... and 69 more

---

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 e84e4d4...4d2481b. Read the comment docs.