CI: Fix installation of homebrew packages

[dweindl]

Things started failing yesterday(?), seemingly because of a pre-installed pkgconf interfering with the one to be installed as hdf5 dependency.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 77.61%. Comparing base (f42cc16) to head (5237787).
Report is 1 commits behind head on develop.

Files with missing lines	Patch %	Lines
python/sdist/amici/__main__.py	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##           develop    #2594       +/-   ##
============================================
+ Coverage    37.11%   77.61%   +40.49%     
============================================
  Files          329      329               
  Lines        21568    22061      +493     
  Branches      1452     1456        +4     
============================================
+ Hits          8006    17123     +9117     
+ Misses       13538     4927     -8611     
+ Partials        24       11       -13     

Flag	Coverage Δ
cpp	73.55% <0.00%> (?)
cpp_python	34.30% <0.00%> (-0.01%)	⬇️
petab	37.23% <0.00%> (-0.01%)	⬇️
python	72.38% <0.00%> (+40.81%)	⬆️

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Files with missing lines	Coverage Δ
python/sdist/amici/__main__.py	0.00% <0.00%> (ø)

... and 253 files with indirect coverage changes

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