Exception when sending email in KernelEvents::TERMINATE event

I added a test that simulates sending mail to reproduce the error.

I don’t really understand why the session was used here, but it seems that every mail sending ends with logs being written and cleared, that is, there is no accumulation at the request level, so I’ll replace the log storage with a regular class property instead of a static one. If I'm wrong, the commit can be deleted.

Setting this to critical since core's Automated Cron is using KernelEvents::TERMINATE, and it is surely common to send emails from cron or queues

This is probably acceptable while while debug is enabled
So checking smtp_debugging before getting smtp_debug from session could also work, patch attached

Here's an updated version of the patch.

I moved the conditionals that would prevent debugging from being logged to the beginning of the method, so we can immediately return. I've also added a call to headers_sent() to avoid accessing the session if TRUE (headers have been sent).