Merged PR 2658: fixed testing for core__check_in_cover_listings

# Description

fixed testing for core__check_in_cover_listings and removed null in accepted values for int_core__bookings in verification_request_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.
- [x] I have checked for DRY opportunities with other models and docs.
- [x] I've picked the right materialization for the affected models.

# Other

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

Related work items: #20229

models/intermediate/core/int_core__check_in_cover_listings.sql

@@ -36,5 +36,5 @@ select
     a.address_line_1,
     cicp.check_in_cover_purchased
 from int_core__check_in_cover_users cicu
-left join int_core__accommodation a on a.id_user_host = cicu.id_user_host
+inner join int_core__accommodation a on a.id_user_host = cicu.id_user_host
 left join check_in_cover_purchased cicp on a.id_accommodation = cicp.id_accommodation

models/intermediate/core/schema.yaml

@@ -1728,7 +1728,6 @@ models:
                   - 'PMS'
                   - 'OSL'
                   - 'API/MANUAL'
-                  - null
 
       - name: id_staging_host_booking
         data_type: bigint