Loading
mapserver: fix mapscript library reference on Darwin
Fix
```
from . import _mapscript
ImportError:
dlopen(/nix/store/av8n3hrg1rs2akhi7b3x3rhn2ksap9fd-mapserver-8.4.1/lib/python3.13/site-packages/mapscript/_mapscript.so,
0x0002): Library not loaded: @rpath/libmapserver.2.dylib
Referenced from: <9D2B480C-B82F-3E1F-93A8-E72C4A175236>
/nix/store/av8n3hrg1rs2akhi7b3x3rhn2ksap9fd-mapserver-8.4.1/lib/python3.13/site-packages/mapscript/_mapscript.so
Reason: no LC_RPATH's found
```
(cherry picked from commit f1165f8e)