fix: onSuccess hook to run after INSTANT

[artemvovk]

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Related issue: #1365

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Description

This PR fixes that no hooks would run after a successful INSTANT DDL, which is an unexpected behavior.

kind of unclear on how to add tests for this because the migrator and hooks tests are very unrelated, but I can try

In case this PR introduced Go code changes:

• contributed code is using same conventions as original code
• script/cibuild returns with no formatting errors, build errors or unit test errors.