Fix macos CI pipeline

[soswow]

Main CI for macos is most likely broken. This PR is where we prove it and fix it.

[soswow]

so, it fails with

 2/12 Test  #2: Test_usage_example_util ..........***Failed    0.80 sec
Failed to save the file: /Users/runner/work/rawtoaces/rawtoaces/build/tests/../../tests/materials/blackmagic_cinema_camera_cinemadng_aces.exr
/Users/runner/work/rawtoaces/rawtoaces/tests/usage_example_util.cpp:42:
FAILED: result
Failed to save the file: /Users/runner/work/rawtoaces/rawtoaces/build/tests/../../tests/materials/blackmagic_cinema_camera_cinemadng_aces.exr
/Users/runner/work/rawtoaces/rawtoaces/tests/usage_example_util.cpp:69:
FAILED: result
ERRORS!

it tries to write back to where code is. In this case at /Users/runner/work/rawtoaces/rawtoaces/tests/materials/blackmagic_cinema_camera_cinemadng_aces.exr and can't do it.
It prob. easy to fix and point it to some definetely writable place like tmp folder.

But what has changed? Why is it suddenly unable to write?

[soswow]

core fix

[codecov-commenter]

Codecov Report

❌ Patch coverage is 25.00000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.53%. Comparing base (a49c1a9) to head (b6f4c12).

Files with missing lines	Patch %	Lines
src/rawtoaces_util/image_converter.cpp	25.00%	3 Missing ⚠️

❌ Your patch status has failed because the patch coverage (25.00%) is below the target coverage (70.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #214      +/-   ##
==========================================
- Coverage   72.62%   72.53%   -0.10%     
==========================================
  Files          10       10              
  Lines        2108     2112       +4     
  Branches      317      317              
==========================================
+ Hits         1531     1532       +1     
- Misses        577      580       +3     

Files with missing lines	Coverage Δ
src/rawtoaces_util/image_converter.cpp	54.65% <25.00%> (-0.12%)	⬇️

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[antond-weta]

LGTM