Update notebook so it uses supplementaries instead of ancillaries

[bouweandela]

Description

Update notebooks/loading-and-processing-data.ipynb so it uses supplementaries instead of ancillaries.

Fix the issue reported in #1924 (comment).

Link to documentation: https://esmvaltool--1945.org.readthedocs.build/projects/ESMValCore/en/1945/notebooks/loading-and-processing-data.html

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[codecov]

Codecov Report

Merging #1945 (5f62dd9) into main (40e00e8) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #1945   +/-   ##
=======================================
  Coverage   92.64%   92.64%           
=======================================
  Files         236      236           
  Lines       12402    12402           
=======================================
  Hits        11490    11490           
  Misses        912      912           

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[valeriupredoi]

cheers @bouweandela = @Peter9192 will you give it a final look and merge, please, mate? 🍺

[Peter9192]

Tested, and It works fine. Just a small comment on one more variable name

[schlunma]

I re-ran all the notebooks, everything works well now 🚀