Main worker should use zadd(xx=True) to update heartbeat

[selwin]

No description provided.

[codecov]

Codecov Report

Merging #1550 (2429ac8) into master (b80045d) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1550      +/-   ##
==========================================
- Coverage   95.54%   95.54%   -0.01%     
==========================================
  Files          46       46              
  Lines        6958     6957       -1     
==========================================
- Hits         6648     6647       -1     
  Misses        310      310              

Impacted Files	Coverage Δ
rq/job.py	98.30% <100.00%> (ø)
rq/registry.py	97.19% <100.00%> (ø)
rq/worker.py	88.64% <100.00%> (ø)
tests/test_cli.py	98.89% <100.00%> (-0.01%)	⬇️

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[aparcar]

Why is this an advantage? And why is this option called xx rather than something like use_zadd?

[selwin]

@aparcar zadd is always used. xx is actually an argument to zadd (I also don't like the option name but that's what Redis calls it). This PR resolves a hard to reproduce race conditions issues reported in #1507

I can maybe rename the option slightly to use_xx

[aparcar]

Thanks for the insights, sorry for the noise