Fix incorrect return statement in auth (#2086)

[kamyabzad]

Pull Request check-list

• Does $ tox pass with this change (including linting)?
• Do the CI tests pass with this change (enable it first in your forked repo and wait for the github action build to finish)?
• Is the new or changed code fully tested?
• Was the change added to CHANGES file?

Description of change

Fix a bug in commands.core.ManagementCommands.auth that returned a function handler when provided with a None username

[codecov-commenter]

Codecov Report

Merging #2092 (226eb22) into master (cb91eed) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@ Coverage Diff @@ ## master #2092 +/- ## ======================================= Coverage 92.45% 92.46% ======================================= Files 104 104 Lines 24364 24365 +1 ======================================= + Hits 22526 22528 +2  + Misses 1838 1837 -1 

Impacted Files	Coverage Δ
redis/commands/core.py	84.04% <100.00%> (+0.03%)	⬆️
tests/test_commands.py	94.32% <100.00%> (+<0.01%)	⬆️

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[chayim]

@kamyabzad thanks for the contribution! Curious what your thoughts are on the suggestion above

[kamyabzad]

@chayim Thanks for the suggestion, I like it more. I have updated the code and the tests (also rebased onto upstream).

[chayim]

@kamyabzad This looks great! I think it's good to merge into the next release.

Thanks again, for both pointing out the issue, and fixing it!

[kamyabzad]

@kamyabzad This looks great! I think it's good to merge into the next release.

Thanks again, for both pointing out the issue, and fixing it!