Fix PYTHONPATH handling in test script for promod3

Author: eunos-1128

Formula/promod3.rb

@@ -48,9 +48,15 @@ def install
     ENV.prepend_path "PYTHONPATH", lib/"python3.13/site-packages"
 
     (testpath/"gen_pdb.py").write <<~EOS
+      import sys
+
       from ost import io
       from promod3 import loop
 
+      site_packages = os.path.join(os.path.dirname(__file__), "..", "lib", "python3.13", "site-packages")
+      site_packages = os.path.abspath(site_packages)
+      sys.path.insert(0, site_packages)
+
       sequence = "HELLYEAH"
       bb_list = loop.BackboneList(sequence)
       io.SavePDB(bb_list.ToEntity(), "test.pdb")