gh-91099: fix[imaplib]: call Exception with string instance

[spaceone]

Adjust the behavior of login() similar to authenticate() where self.error is called with a str instance.

Especially for Python3 with strict bytes mode (-bb) this is helpful and prevents:

    Traceback (most recent call last):
      in "<stdin>"
        self.login(email, password)
      File "/usr/lib/python3.7/imaplib.py", line 598, in login
        raise self.error(dat[-1])
    imaplib.error: <exception str() failed>
    
    During handling of the above exception, another exception occurred:
    Traceback (most recent call last):
      in "<stdin>"
        str(exc)
    BytesWarning: str() on a bytes instance

https://bugs.python.org/issue46943

• Issue: fix[imaplib]: call Exception with string instance #91099

[cpython-cla-bot]

All commit authors signed the Contributor License Agreement.

[arhadthedev]

@spaceone Could you sign the new CLA by clicking not signed button in the cpython-cla-bot's message, please?

[spaceone]

@spaceone Could you sign the new CLA by clicking not signed button in the cpython-cla-bot's message, please?

I tried but get a white screen with Internal Server Error. Will retry later in the evening with another browser.

[arhadthedev]

No worries, your click was accepted. The displayed error is a known although yet untracked problem.

[arhadthedev]

@python/email-team