test_gaussian fails for fedora rawhide

[jdkloe]

For fedora-rawhide (to be fedora-41) software versions have been updated to be:
Python version 3.13.0b3
matplotlib version 3.9.1
eccodes version 2.35.0

For these versions, all tests pass except for test_gaussian:

# pytest test_gaussian.py --mpl --mpl-baseline-path=`pwd`/baseline_images
================================== test session starts ===================================
platform linux -- Python 3.13.0b3, pytest-7.4.3, pluggy-1.3.0
Matplotlib: 3.9.1
Freetype: 2.13.2
rootdir: /builddir/build/BUILD/pygrib-2.1.6-build/pygrib-2.1.6-tmp-test/test
plugins: mpl-0.13
collected 1 item                                                                         

test_gaussian.py F                                                                 [100%]

======================================== FAILURES ========================================
_____________________________________ test_gaussian ______________________________________
Error: Image files did not match.
  RMS Value: 31.307504414099967
  Expected:  
    /tmp/tmpolc15yoq/test_gaussian.test_gaussian/baseline.png
  Actual:    
    /tmp/tmpolc15yoq/test_gaussian.test_gaussian/result.png
  Difference:
    /tmp/tmpolc15yoq/test_gaussian.test_gaussian/result-failed-diff.png
  Tolerance: 
    20
================================ short test summary info =================================
FAILED test_gaussian.py::test_gaussian - Failed: Error: Image files did not match.
=================================== 1 failed in 1.16s ====================================

From visual inspection of the generated image it is clear that the generated image has been shifted upwards by a few pixels compared to the baseline reference inside its black framing rectangle, and this framing rectangle has at the same time increased size by a few pixels. The picture itself is still identical to the baseline.

As a workaround in the mpl_image_compare decorator, the tolerance can be increased from 20 to 32. Then the test passes again.