Add experimental 3.12 tests

[Dreamsorcerer]

3.12 release candidate should be out next week, so we can start preparing releases for 3.12.

[codecov]

Codecov Report

Merging #7400 (354c06f) into master (0b34147) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #7400   +/-   ##
=======================================
  Coverage   97.28%   97.28%           
=======================================
  Files         106      106           
  Lines       31440    31440           
  Branches     3932     3932           
=======================================
  Hits        30585    30585           
  Misses        650      650           
  Partials      205      205           

Flag	Coverage Δ
CI-GHA	97.22% <ø> (ø)
OS-Linux	96.89% <ø> (ø)
OS-Windows	95.35% <ø> (ø)
OS-macOS	96.58% <ø> (ø)
Py-3.10.11	95.27% <ø> (ø)
Py-3.10.12	96.79% <ø> (ø)
Py-3.11.0	?
Py-3.11.4	96.51% <ø> (?)
Py-3.8.10	95.24% <ø> (ø)
Py-3.8.17	96.72% <ø> (ø)
Py-3.9.13	95.24% <ø> (ø)
Py-3.9.17	96.75% <ø> (ø)
Py-pypy7.3.11	94.20% <ø> (ø)
VM-macos	96.58% <ø> (ø)
VM-ubuntu	96.89% <ø> (ø)
VM-windows	95.35% <ø> (ø)

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[Dreamsorcerer]

Still needs a few more fixes, but they can be done in later PRs.

[patchback]

Backport to 3.9: 💔 cherry-picking failed — conflicts found

❌ Failed to cleanly apply 972c002 on top of patchback/backports/3.9/972c002c53040d65954d8ebb1e8e015ba2fdd2f4/pr-7400

Backporting merged PR #7400 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 remote add 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/3.9/972c002c53040d65954d8ebb1e8e015ba2fdd2f4/pr-7400 upstream/3.9

4. Now, cherry-pick PR Add experimental 3.12 tests #7400 contents into that branch:

   $ git cherry-pick -x 972c002c53040d65954d8ebb1e8e015ba2fdd2f4

   If it'll yell at you with something like fatal: Commit 972c002c53040d65954d8ebb1e8e015ba2fdd2f4 is a merge but no -m option was given., add -m 1 as follows instead:

   $ git cherry-pick -m1 -x 972c002c53040d65954d8ebb1e8e015ba2fdd2f4

5. At this point, you'll probably encounter some merge conflicts. You must
   resolve them in to preserve the patch from PR Add experimental 3.12 tests #7400 as close to the
   original as possible.
6. Push this branch to your fork on GitHub:

   $ git push origin patchback/backports/3.9/972c002c53040d65954d8ebb1e8e015ba2fdd2f4/pr-7400

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
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