fix: add missing deprecation_date field to models schema

[nicnic65]

The deprecation_date field is a new model property added in v1.6 per upgrade notes here.

This field is supported in all dbt-core versions >=1.6, docs here:

• https://docs.getdbt.com/reference/resource-properties/deprecation_date
• https://docs.getdbt.com/reference/model-properties