Add filterwarning for jax.tree_multimap

[marcvanzee]

See #2037

What does this PR do?

Fixes # (issue)

Checklist

• This PR fixes a minor issue (e.g.: typo or small bug) or improves the docs (you can dismiss the other
  checks if that's the case).
• This change is discussed in a Github issue/
  discussion (please add a
  link).
• The documentation and docstrings adhere to the
  documentation guidelines.
• This change includes necessary high-coverage tests.
  (No quality testing = no merge!)

[codecov-commenter]

Codecov Report

Merging #2038 (181bcaa) into main (871358a) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #2038   +/-   ##
=======================================
  Coverage   74.86%   74.86%           
=======================================
  Files          59       59           
  Lines        5037     5037           
=======================================
  Hits         3771     3771           
  Misses       1266     1266           

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