Add support in the redis result backend for authenticating with a username

[thedrow]

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Description

Previously, the username was ignored from the URI.
Starting from Redis>=6.0, that shouldn't be the case since ACL support has landed.

Fixes #6422.

[codecov]

Codecov Report

Merging #6750 (398eaad) into master (0953a4d) will increase coverage by 0.18%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #6750      +/-   ##
==========================================
+ Coverage   70.50%   70.69%   +0.18%     
==========================================
  Files         138      138              
  Lines       16485    16559      +74     
  Branches     2065     2079      +14     
==========================================
+ Hits        11623    11706      +83     
+ Misses       4660     4658       -2     
+ Partials      202      195       -7     

Flag	Coverage Δ
unittests	70.69% <100.00%> (+0.18%)	⬆️

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

Impacted Files	Coverage Δ
celery/app/defaults.py	97.33% <ø> (ø)
celery/backends/redis.py	82.95% <100.00%> (+0.14%)	⬆️
celery/worker/request.py	96.91% <0.00%> (-0.03%)	⬇️
celery/app/amqp.py	94.09% <0.00%> (ø)
celery/app/base.py	58.93% <0.00%> (ø)
celery/bin/amqp.py	0.00% <0.00%> (ø)
celery/app/utils.py	47.61% <0.00%> (ø)
celery/bin/control.py	0.00% <0.00%> (ø)
celery/app/task.py	93.83% <0.00%> (+0.01%)	⬆️
... and 6 more

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[lgtm-com]

This pull request introduces 1 alert and fixes 2 when merging b93fe34 into b0326ab - view on LGTM.com

new alerts:

• 1 for Unused import

fixed alerts:

• 1 for Non-exception in 'except' clause
• 1 for Module is imported with 'import' and 'import from'

[thedrow]

@auvipy I addressed your comment.
I'm merging this per your previous review as I want to expedite releasing beta 2.

[lgtm-com]

This pull request introduces 1 alert and fixes 2 when merging 398eaad into b0326ab - view on LGTM.com

new alerts:

• 1 for Unused import

fixed alerts:

• 1 for Non-exception in 'except' clause
• 1 for Module is imported with 'import' and 'import from'

[auvipy]

sure.