title: cryptography not loading openssl certificate
body: <p>with that I have created an openssl key and certificate</p>
  <pre><code>openssl req -x509 -nodes -days 365 -newkey rsa:2048 -keyout test.key -out test.cert
  </code></pre>
  <p>with that I would like to load the certificate</p>
  <pre><code>from cryptography import x509
  cert = x509.load_pem_x509_certificate('test.cert')
  </code></pre>
  <p>but failed with that exception</p>
  <pre><code>line 636, in _bytes_to_bio
  data_ptr = self._ffi.from_buffer(data)
  TypeError: from_buffer() cannot return the address of a unicode object
  </code></pre>
  <p>as far I can see I followed the documentation. How would I correctly create/use x509 certs with python &gt;=3.8 ?</p>