fix: Restore response_class on every request to prevent status leak

[ubaskota]

Issue #, if available: #3755

Description of changes:
AWSConnection.request() only restored the response_class override in the non-Expect branch, so a cached status from an early final response could leak onto the next request on a pooled connection, dropping its headers (e.g. a missing S3 ETag). Move the restore so it runs on every request.

Testing

• Verified that the newly added test passes with the fix and fails without it.
• Verified that the existing passes

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.47%. Comparing base (ee748e4) to head (d887614).
⚠️ Report is 477 commits behind head on develop.
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Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #3784      +/-   ##
===========================================
- Coverage    92.59%   92.47%   -0.13%     
===========================================
  Files           68       68              
  Lines        15634    15859     +225     
===========================================
+ Hits         14477    14666     +189     
- Misses        1157     1193      +36     

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