Fix the PDF build of the documentation

[bouweandela]

Description

Closes #3067

Link to documentation builds for this branch: https://app.readthedocs.org/projects/esmvalcore/builds/?version__slug=fix-pdf-build
Link to the PDF: https://docs.esmvaltool.org/_/downloads/ESMValCore/en/fix-pdf-build/pdf/

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.15%. Comparing base (e232092) to head (c64309e).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3068   +/-   ##
=======================================
  Coverage   96.15%   96.15%           
=======================================
  Files         270      270           
  Lines       15807    15807           
=======================================
  Hits        15200    15200           
  Misses        607      607           

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[bouweandela]

With these changes, the PDF documentation builds, but there are errors in the latex command. Need to investigate if these were previously already there and if they are important.