Empty except

[pepoluan]

So basically in the examples we have some try..except, and there's an except KeyboardInterrupt: that has nothing but a pass in it.

CodeQL complained about this, either we put something there and/or add a comment there.

Affected files:

• examples/authenticated_relayer/server.py
• examples/basic/server.py

Tracking issue for:

• [ ] https://github.com/aio-libs/aiosmtpd/security/code-scanning/6
• [ ] https://github.com/aio-libs/aiosmtpd/security/code-scanning/7