Improve get_data_in_units docstring

[rly]

Follow-up to #1878 to fix a broken link and clarify the docstring further to reflect the behavior of channel_conversion.

Checklist

• Did you update CHANGELOG.md with your changes?
• Have you checked our Contributing document?
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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.81%. Comparing base (9af54a2) to head (f168907).

Additional details and impacted files

@@           Coverage Diff           @@
##              dev    #1880   +/-   ##
=======================================
  Coverage   91.81%   91.81%           
=======================================
  Files          27       27           
  Lines        2627     2627           
  Branches      688      688           
=======================================
  Hits         2412     2412           
  Misses        142      142           
  Partials       73       73           

Flag	Coverage Δ
integration	72.47% <ø> (ø)
unit	83.82% <ø> (ø)

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