clustering: fix column selection in aggregateoneport

[FabianHofmann]

Related to current CI fails in pypsa-eur

Checklist

• Code changes are sufficiently documented; i.e. new functions contain docstrings and further explanations may be given in doc.
• Unit tests for new features were added (if applicable).
• Newly introduced dependencies are added to environment.yaml, environment_docs.yaml and setup.py (if applicable).
• A note for the release notes doc/release_notes.rst of the upcoming release is included.
• I consent to the release of this PR's code under the MIT license.

[codecov]

Codecov Report

Patch coverage: 33.33% and no project coverage change.

Comparison is base (0b62fbb) 78.14% compared to head (dac95d0) 78.14%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #696   +/-   ##
=======================================
  Coverage   78.14%   78.14%           
=======================================
  Files          26       26           
  Lines        6764     6764           
  Branches     1467     1467           
=======================================
  Hits         5286     5286           
  Misses       1165     1165           
  Partials      313      313           

Files Changed	Coverage Δ
pypsa/clustering/spatial.py	66.55% <33.33%> (ø)

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