Fix tests that don't throw DeprecationWarning

[atemate]

Fixed two old tests that assert throwing DeprecationWarning whereas in fact the AttributeError is raised. These tests start to be wrong since the RequestHandler.__slots__ were implemented (see #3095).

What do these changes do?

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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
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• Add a new news fragment into the CHANGES folder
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  • if you don't have an issue_id change it to the pr id after creating the pr
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    • .feature: Signifying a new feature.
    • .bugfix: Signifying a bug fix.
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    • .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-io]

Codecov Report

Merging #3738 into master will decrease coverage by 3.07%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3738      +/-   ##
==========================================
- Coverage   97.89%   94.82%   -3.08%     
==========================================
  Files          43       43              
  Lines        8558     8557       -1     
  Branches     1377     1376       -1     
==========================================
- Hits         8378     8114     -264     
- Misses         75      338     +263     
  Partials      105      105

Impacted Files	Coverage Δ
aiohttp/worker.py	6.55% <0%> (-90.99%)	⬇️
aiohttp/resolver.py	46.55% <0%> (-53.45%)	⬇️
aiohttp/web_fileresponse.py	66.66% <0%> (-29.89%)	⬇️
aiohttp/tcp_helpers.py	63.33% <0%> (-26.67%)	⬇️
aiohttp/locks.py	92.85% <0%> (-7.15%)	⬇️
aiohttp/web_runner.py	91.7% <0%> (-6.22%)	⬇️
aiohttp/__init__.py	94.44% <0%> (-5.56%)	⬇️
aiohttp/http_parser.py	93.11% <0%> (-4.82%)	⬇️
aiohttp/http_writer.py	95.28% <0%> (-2.84%)	⬇️
aiohttp/frozenlist.py	97.87% <0%> (-2.13%)	⬇️
... and 5 more

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[asvetlov]

please drop unused imports

[CLAassistant]

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✅ asvetlov
❌ ayushkovskiy
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