Make check for existing user in custos_authnz.py case insensitive

import jwt

from oauthlib.common import generate_nonce

from requests_oauthlib import OAuth2Session

from sqlalchemy import func

from galaxy import (

    exceptions,

        custos_authnz_token = self._get_custos_authnz_token(trans.sa_session, user_id, self.config.provider)

        if custos_authnz_token is None:

            user = trans.user

            existing_user = trans.sa_session.query(User).filter_by(email=email).first()

            existing_user = trans.sa_session.query(User).filter(func.lower(User.email) == email.lower()).first()

            if not user:

                if existing_user:

                    if trans.app.config.fixed_delegated_auth: