Fix potential test gap in SM DA

[rajatagarwal-ibm]

Potential test gap:

Test SM DA provision using an existing SM instance. For example https://github.com/terraform-ibm-modules/experimental-terraform-ibm-event-notifications/blob/main/tests/pr_test.go#L271

[ocofaigh]

@rajatagarwal-ibm A test is add in #300

[Aayush-Abhyarthi]

PR merged.