title: pybind11 import_ not working in debug mode for external library
body: <p>In a C++ project (with Visual Studio 2019) I am loading a python library (my_external_library) for some data processing.
  When it runs in Release Mode, everything is fine.
  Instead, in Debug mode, the module import_ from pybind11 crashes</p>
  <pre><code>  C:\Program Files (x86)\Microsoft Visual Studio\Shared\Python39_64\lib\site-packages\my_external_library\__init__.py(1): &lt;module&gt;
    &lt;frozen importlib._bootstrap&gt;(228): _call_with_frames_removed
    &lt;frozen importlib._bootstrap_external&gt;(850): exec_module
    &lt;frozen importlib._bootstrap&gt;(695): _load_unlocked
    &lt;frozen importlib._bootstrap&gt;(986): _find_and_load_unlocked
    &lt;frozen importlib._bootstrap&gt;(1007): _find_and_load
    &lt;frozen importlib._bootstrap&gt;(228): _call_with_frames_removed
    &lt;frozen importlib._bootstrap&gt;(972): _find_and_load_unlocked
    &lt;frozen importlib._bootstrap&gt;(1007): _find_and_load
  </code></pre>
  <p>Further, note that I have also tried to load <code>numpy</code> and I get the same error in debug mode (release mode is fine), whilst if I run the <code>sys</code> library everything is fine in both debug and release mode.</p>
  <p>Any idea of why is like this?</p>