[WIP] fix mst concatenator bug seen in example notebook

[atravitz]

resolves #202

PR Author Checklist

• added news item, or changes are not user-facing
• pre-commit CI passes (comment pre-commit.ci autofix to auto-format your PR).

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• I certify that this contribution is covered by the MIT License here and the Developer Certificate of Origin at https://developercertificate.org/.

Reviewer Checklist

• news entry has been added if necessary
• pre-commit auto fix has been run
• any API breaks have been documented

[codecov]

Codecov Report

❌ Patch coverage is 75.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 92.21%. Comparing base (527c712) to head (6adcda4).

Files with missing lines	Patch %	Lines
.../konnektor/tests/network_tools/test_concatenate.py	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #201      +/-   ##
==========================================
- Coverage   92.24%   92.21%   -0.03%     
==========================================
  Files          84       84              
  Lines        2618     2622       +4     
==========================================
+ Hits         2415     2418       +3     
- Misses        203      204       +1     

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[atravitz]

NOTE: add the advanced topics notebook back to the docs once this is fixed.