UT: Mock `open()` in PowerShellExploiter tests instead of using `monkeyfs`

monkey/tests/unit_tests/infection_monkey/exploit/test_powershell.py

@@ -48,10 +48,7 @@ def powershell_exploiter(monkeypatch):
 
     monkeypatch.setattr(powershell, "AuthenticationError", AuthenticationErrorForTests)
     monkeypatch.setattr(powershell, "is_windows_os", lambda: True)
-    # It's regrettable to mock out a private method on the PowerShellExploiter instance object, but
-    # it's necessary to avoid having to deal with the monkeyfs. TODO: monkeyfs has been removed, so
-    # fix this.
-    # monkeypatch.setattr(pe, "_create_local_agent_file", lambda: None)
+    monkeypatch.setattr("builtins.open", lambda _, __: MagicMock())
 
     return pe