Fix cookie handling

[bratao]

What do these changes do?

There is an error in cookie handling that override the existing cookie even if the path is different. This is a huge bug in aiohttp, as it makes requests to some sites impossible to work.

This is an updated PR as asked by @Dreamsorcerer

The RFC 6265 is clear on this point (https://datatracker.ietf.org/doc/html/rfc6265) , for example:

Finally, to remove a cookie, the server returns a Set-Cookie header
   with an expiration date in the past.  The server will be successful
   in removing the cookie only **if the Path and the Domain attribute** in
   the Set-Cookie header match the values used when the cookie was
   created.

Actually aiohttp only consider domain and name. Pull request #3627 tried to fix this, but the code has been updated vastly since then.

Pay attention to another library, such as requests. It always consider the path as a key to the cookie jar.
https://github.com/psf/requests/blob/79f60274f7e461b8fd2f579e741f748438d7eadb/requests/cookies.py#L189

Are there changes in behavior for the user?

No

Related issue number

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 #6638 (58ed64f) into master (b19d559) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #6638   +/-   ##
=======================================
  Coverage   93.36%   93.36%           
=======================================
  Files         104      104           
  Lines       30624    30637   +13     
  Branches     3080     3080           
=======================================
+ Hits        28592    28605   +13     
  Misses       1859     1859           
  Partials      173      173           

Flag	Coverage Δ
unit	93.28% <100.00%> (+<0.01%)	⬆️

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

Impacted Files	Coverage Δ
aiohttp/cookiejar.py	98.83% <100.00%> (ø)
tests/test_cookiejar.py	99.09% <100.00%> (+0.03%)	⬆️

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[Dreamsorcerer]

If no one else reviews, I'll merge it at the weekend.

[patchback]

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

❌ Failed to cleanly apply 916b3ee on top of patchback/backports/3.9/916b3eecda825cd42415b6f8821c035647baf890/pr-6638

Backporting merged PR #6638 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/3.9/916b3eecda825cd42415b6f8821c035647baf890/pr-6638 upstream/3.9

4. Now, cherry-pick PR Fix cookie handling #6638 contents into that branch:

   $ git cherry-pick -x 916b3eecda825cd42415b6f8821c035647baf890

   If it'll yell at you with something like fatal: Commit 916b3eecda825cd42415b6f8821c035647baf890 is a merge but no -m option was given., add -m 1 as follows intead:

   $ git cherry-pick -m1 -x 916b3eecda825cd42415b6f8821c035647baf890

5. At this point, you'll probably encounter some merge conflicts. You must
   resolve them in to preserve the patch from PR Fix cookie handling #6638 as close to the
   original as possible.
6. Push this branch to your fork on GitHub:

   $ git push origin patchback/backports/3.9/916b3eecda825cd42415b6f8821c035647baf890/pr-6638

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.

[Dreamsorcerer]

If you could handle the backport to 3.9 (as per instructions above), that would be great.