Add default None for maxlen at xtrim command

[mfgnik]

Pull Request check-list

Please make sure to review and check all of these items:

• 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?
• Is a documentation update included (if this change modifies existing APIs, or introduces new ones)?
• Is there an example added to the examples folder (if applicable)?
• Was the change added to CHANGES file?

NOTE: these things are not required to open a PR and can be done
afterwards / while the PR is open.

Description of change

Please provide a description of the change here.

[dvora-h]

Thanks @mfgnik ! I just merged in the latest master- it all passes, and we’ll merge this in.

[codecov-commenter]

Codecov Report

Merging #2188 (4c46715) into master (bac33d4) will increase coverage by 0.00%.
The diff coverage is 50.00%.

@@           Coverage Diff           @@
##           master    #2188   +/-   ##
=======================================
  Coverage   92.03%   92.03%           
=======================================
  Files         108      108           
  Lines       27629    27631    +2     
=======================================
+ Hits        25427    25430    +3     
+ Misses       2202     2201    -1     

Impacted Files	Coverage Δ
redis/commands/core.py	82.95% <50.00%> (-0.04%)	⬇️
tests/test_cluster.py	97.14% <0.00%> (+0.11%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update bac33d4...4c46715. Read the comment docs.