When you have Custom Connection and use SelectField, Connection screen becomes unusable (see #17064) 

We should detect the situation and throw an exception when Provider Info is initialized.
airflow/providers_manager.py
try:
            connection_type = getattr(hook_class, "conn_type")
            self._customized_form_fields_schema_validator.validate(customized_fields)
            if connection_type in self._field_behaviours:
                log.warning(
                    "The connection_type %s from package %s and class %s has already been added "
                    "by another provider. Ignoring it.",
                    connection_type,
                    package_name,
                    hook_class.__name__,
                )
                return
            self._field_behaviours[connection_type] = customized_fields
        except Exception as e:
            log.warning(
                "Error when loading customized fields from package '%s' hook class '%s': %s",
                package_name,
                hook_class.__name__,
                e,
            )
    def _discover_extra_links(self) -> None: