Log clients speaking HTTP on the HTTPS port

This patch extends the processing of a case when a client attempts
sending plain HTTP into an HTTPS port by emitting a log message.

cheroot/connections.py

@@ -299,7 +299,13 @@ def _from_server_socket(self, server_socket): # noqa: C901 # FIXME
  f'{tls_connection_drop_error !s}',
  )
  return
- except errors.NoSSLError:
+ except errors.NoSSLError as http_over_https_err:
+ self.server.error_log(
+ f'Client {addr !s} attempted to speak plain HTTP into '
+ 'a TCP connection configured for TLS-only traffic — '
+ 'trying to send back a plain HTTP error response: '
+ f'{http_over_https_err !s}',
+ )
  msg = (
  'The client sent a plain HTTP request, but '
  'this server only speaks HTTPS on this port.'