Fix the link to MultiDict in client_quickstart.rst

[webknjaz]

What do these changes do?

This change corrects an unrendered intersphinx class reference in the client_quickstart.rst document.

Are there changes in behavior for the user?

Related issue number

#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 #5517 (4945527) into master (25dfe50) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #5517   +/-   ##
=======================================
  Coverage   97.17%   97.17%           
=======================================
  Files          41       41           
  Lines        8854     8854           
  Branches     1424     1424           
=======================================
  Hits         8604     8604           
  Misses        133      133           
  Partials      117      117           

Flag	Coverage Δ
unit	97.06% <ø> (ø)

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[patchback]

Backport to 3.8: 💔 cherry-picking failed — conflicts found

❌ Failed to cleanly apply 13fd83e on top of patchback/backports/3.8/13fd83ee73aa584174ebe3b8c4e19e4c5fcddfd7/pr-5517

Backporting merged PR #5517 into master

1. Ensure you have a local repo clone of your fork. Unless you cloned it
   from the upstream, this would be your origin remote.
2. Make sure you have an upstream repo added as a remote too. In these
   instructions you'll refer to it by the name upstream. If you don't
   have it, here's how you can add it:

   $ git add remote upstream https://github.com/aio-libs/aiohttp.git

3. Ensure you have the latest copy of upstream and prepare a branch
   that will hold the backported code:

   $ git fetch upstream
   $ git checkout -b patchback/backports/3.8/13fd83ee73aa584174ebe3b8c4e19e4c5fcddfd7/pr-5517 upstream/3.8

4. Now, cherry-pick PR Fix the link to MultiDict in client_quickstart.rst #5517 contents into that branch:

   $ git cherry-pick -x 13fd83ee73aa584174ebe3b8c4e19e4c5fcddfd7

   If it'll yell at you with something like fatal: Commit 13fd83ee73aa584174ebe3b8c4e19e4c5fcddfd7 is a merge but no -m option was given., add -m 1 as follows intead:

   $ git cherry-pick -m1 -x 13fd83ee73aa584174ebe3b8c4e19e4c5fcddfd7

5. At this point, you'll probably encounter some merge conflicts. You must
   resolve them in to preserve the patch from PR Fix the link to MultiDict in client_quickstart.rst #5517 as close to the
   original as possible.
6. Push this branch to your fork on GitHub:

   $ git push origin patchback/backports/3.8/13fd83ee73aa584174ebe3b8c4e19e4c5fcddfd7/pr-5517

7. Create a PR, ensure that the CI is green. If it's not — update it so that
   the tests and any other checks pass. This is it!
   Now relax and wait for the maintainers to process your pull request
   when they have some cycles to do reviews. Don't worry — they'll tell you if
   any improvements are necessary when the time comes!

🤖 @patchback
I'm built with octomachinery and
my source is open — https://github.com/sanitizers/patchback-github-app.