SQLAlchemy: Improve error message when using schema query parameter twice

[amotl]

Problem

When approaching the CrateDB SQLAlchemy dialect with an erroneous connection string including the schema query parameter twice, like crate://localhost/?schema=foo&schema=bar, it fails using this exception message:

(crate.client.exceptions.ProgrammingError) expected string or bytes-like object, got 'tuple'

The error message may be improved.

References

• AutoML: Improve notebooks for easier usage on Google Colab cratedb-examples#174 (review)