Add xfailing integration tests against proxy.py

[bmbouter]

I was running this with pytest 'tests/test_proxy_functional.py::test_secure_proxy_http_absolute_path'

I tried using the TestCase from proxy.py but I want these as pytest fixtures and I couldn't find a way to call the trustme fixture and set the class attributes I need to here. So instead I'm "doing it like their TestCase" only as a fixture. This probably should go into proxy.py eventually, but here it is for now.

[bmbouter]

I was running these with:

pytest --log-level=INFO 'tests/test_proxy_functional.py::test_secure_proxy_http_absolute_path'
pytest --log-level=INFO 'tests/test_proxy_functional.py::test_secure_proxy_https_absolute_path'

[bmbouter]

@webknjaz this is as far as I could take these tests. I spent a long time messing with it. I'm hoping you can take it from here. Also FYI @dkliban.

[codecov]

Codecov Report

Merging #6002 (1edb61a) into master (e445011) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #6002   +/-   ##
=======================================
  Coverage   96.75%   96.75%           
=======================================
  Files          44       44           
  Lines        9857     9857           
  Branches     1592     1592           
=======================================
  Hits         9537     9537           
  Misses        182      182           
  Partials      138      138           

Flag	Coverage Δ
unit	96.65% <ø> (ø)

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[patchback]

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

❌ Failed to cleanly apply d66e07c on top of patchback/backports/3.8/d66e07c652322d280740106ebb9946a3dd7daf5b/pr-6002

Backporting merged PR #6002 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/3.8/d66e07c652322d280740106ebb9946a3dd7daf5b/pr-6002 upstream/3.8

4. Now, cherry-pick PR Add xfailing integration tests against proxy.py #6002 contents into that branch:

   $ git cherry-pick -x d66e07c652322d280740106ebb9946a3dd7daf5b

   If it'll yell at you with something like fatal: Commit d66e07c652322d280740106ebb9946a3dd7daf5b is a merge but no -m option was given., add -m 1 as follows intead:

   $ git cherry-pick -m1 -x d66e07c652322d280740106ebb9946a3dd7daf5b

5. At this point, you'll probably encounter some merge conflicts. You must
   resolve them in to preserve the patch from PR Add xfailing integration tests against proxy.py #6002 as close to the
   original as possible.
6. Push this branch to your fork on GitHub:

   $ git push origin patchback/backports/3.8/d66e07c652322d280740106ebb9946a3dd7daf5b/pr-6002

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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