Merged PR 4852: removed test of not_null

# Description

Removing not_null test for `booking_source`

# Checklist

- [x] The edited models and dependants run properly with production data.
- [x] The edited models are sufficiently documented.
- [x] The edited models contain PK tests, and I've ran and passed them.
- [ ] I have checked for DRY opportunities with other models and docs.
- [ ] I've picked the right materialization for the affected models.

# Other

- [ ] Check if a full-refresh is required after this PR is merged.

removed test of not_null

models/intermediate/core/schema.yml

@@ -1210,7 +1210,6 @@ models:
           - OSL
           - API/MANUAL
         data_tests:
-          - not_null
           - accepted_values:
               values:
                 - "PMS"

models/reporting/core/schema.yml

@@ -872,7 +872,6 @@ models:
           - OSL
           - API/MANUAL
         data_tests:
-          - not_null
           - accepted_values:
               values:
                 - "PMS"