Fix: check for None instead of false value in sort_ref_id (current line raises exception if electrode 0 is set to reference)

[sharon-chiang]

Description

• Fix: Checks for None instead of false value.
  • src/spyglass/spikesorting/utils.py: Change to check for is None rather than not. I think this should fix the issue.

Checklist:

• NA If this PR should be accompanied by a release, I have updated the CITATION.cff
• NA If this PR edits table definitions, I have included an alter snippet for release notes.
• NA If this PR makes changes to position, I ran the relevant tests locally.
• NA If this PR makes user-facing changes, I have added/edited docs/notebooks to reflect the changes
• NA I have updated the CHANGELOG.md with PR number and description.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.12%. Comparing base (be9314f) to head (fe4c77d).
⚠️ Report is 19 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1480      +/-   ##
==========================================
+ Coverage   70.54%   71.12%   +0.58%     
==========================================
  Files         104      114      +10     
  Lines       12650    13306     +656     
==========================================
+ Hits         8924     9464     +540     
- Misses       3726     3842     +116     

Flag	Coverage Δ
full-tests	71.12% <ø> (?)

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