Handle removed is_rgb from fmt 11.2.0

[Hind-M]

Description

Fix #3958

Type of Change

• Bugfix
• Feature / enhancement
• CI / Documentation
• Maintenance

Checklist

• My code follows the general style and conventions of the codebase, ensuring consistency
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• I have run pre-commit run --all locally in the source folder and confirmed that there are no linter errors.
• I have added tests that prove my fix is effective or that my feature works
• New and existing tests pass locally with my changes

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.

Project coverage is 63.81%. Comparing base (6adb2ea) to head (198fc53).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
libmambapy/src/libmambapy/bindings/utils.cpp	0.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3998      +/-   ##
==========================================
- Coverage   63.81%   63.81%   -0.01%     
==========================================
  Files         303      303              
  Lines       38673    38675       +2     
  Branches     2865     2858       -7     
==========================================
+ Hits        24681    24682       +1     
- Misses      13925    13926       +1     
  Partials       67       67              

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[jjerphan]

LGTM. Thank you, @Hind-M.

Side-note: we could ask to merge conda-forge/fmt-feedstock#66 to test the other case.