test/gen.py fail on MacOs Catalina

On a fresh install of MacOs Catalina (with dev tools + macports), the folowing error is raised when running gen.py

Traceback (most recent call last):
  File "gen.py", line 24, in <module>
    import spot.gen as gen
  File "/Users/etienne/src/spot/python/spot/gen.py", line 13, in <module>
    from . import _gen
ImportError: dlopen(/Users/etienne/src/spot/python/spot/.libs/_gen.so, 2): Library not loaded: /usr/local/lib/libspotgen.0.dylib
  Referenced from: /Users/etienne/src/spot/python/spot/.libs/_gen.so
  Reason: image not found
FAIL python/gen.py (exit status: 1)

I suspect (again) compatibility problems between *.dylib and *.so

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