Extend deprovisioning notification test

[saw-jan]

Follow up #6994

Extend deprovisioning notification test.

Test cases:

• using different date format (deprovision_date_format)@nirajacharya2

curl -XPOST -vk -uadmin:admin \
-d '{"type":"deprovision", "data":{"deprovision_date": "Mon Jan 2 15:04:05 MST 2023", "deprovision_date_format":"Mon Jan _2 15:04:05 MST 2006"}}' \
https://localhost:9200/ocs/v2.php/apps/notifications/api/v1/notifications/global

• https://pkg.go.dev/time#pkg-constants
• change notification (another POST request with a different date)