fix: Set PYTHONPATH in env.run_ret_code call in FBWorkspace class (#755)

Author: you-n-g

rdagent/core/experiment.py

@@ -261,7 +261,7 @@ def execute_ret_code(self, env: Env, entry: str) -> tuple[str, int]:
         """
         self.prepare()
         self.inject_files(**self.file_dict)
-        stdout, return_code = env.run_ret_code(entry, str(self.workspace_path))
+        stdout, return_code = env.run_ret_code(entry, str(self.workspace_path), env={"PYTHONPATH": "./"})
         return (
             shrink_text(
                 filter_redundant_text(stdout),