Fix varying cmake libdir lib(64)/

[dweindl]

Some systems use lib/, some lib64/.

Just adding the amici package base dir to CMAKE_PREFIX_PATH doesn't suffice to find FindSuiteSparse_config.cmake.

[codecov]

Codecov Report

Merging #2033 (ecd6bbb) into develop (ecd6bbb) will not change coverage.
The diff coverage is n/a.

❗ Current head ecd6bbb differs from pull request most recent head 140f692. Consider uploading reports for the commit 140f692 to get more accurate results

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #2033   +/-   ##
========================================
  Coverage    71.74%   71.74%           
========================================
  Files           72       72           
  Lines        12921    12921           
========================================
  Hits          9270     9270           
  Misses        3651     3651           

Flag	Coverage Δ
cpp	72.85% <0.00%> (ø)
python	69.62% <0.00%> (ø)

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