Fix sync stream bug in SpikeGLXConverterPipe

[h-mayorquin]

Now that the sync stream is separated on neo we need this safeguard:

NeuralEnsemble/python-neo#1683

[pauladkisson]

Looks good to me!

[codecov]

Codecov Report

❌ Patch coverage is 83.33333% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 89.95%. Comparing base (6ad8695) to head (19b6b07).
⚠️ Report is 66 commits behind head on main.

Files with missing lines	Patch %	Lines
...terfaces/ecephys/spikeglx/spikeglxdatainterface.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1373      +/-   ##
==========================================
- Coverage   89.96%   89.95%   -0.01%     
==========================================
  Files         141      141              
  Lines        9096     9100       +4     
==========================================
+ Hits         8183     8186       +3     
- Misses        913      914       +1     

Flag	Coverage Δ
unittests	89.95% <83.33%> (-0.01%)	⬇️

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

Files with missing lines	Coverage Δ
...tainterfaces/ecephys/spikeglx/spikeglxconverter.py	92.10% <100.00%> (+0.43%)	⬆️
...terfaces/ecephys/spikeglx/spikeglxdatainterface.py	94.36% <50.00%> (-1.29%)	⬇️

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