Prevent timor from crashing when cobra schemata are not resolvable

At the moment, Timor is basically unusable due to a cobra API error. (see e.g. https://gitlab.lrz.de/tum-cps/timor-python/-/jobs/6387739)

https://cobra.cps.cit.tum.de/api/schemas/CoBRABaseSchema.json is broken which causes errors in any schema validation.

This MR prevents failure and only issues a warning.