Fix failing tests for CloudSQL

[wiktorn]

Adding dependency on the IAM grant, because on destroy, if the grant is removed before instance is deleted, instance deletion fails 🤷:

Error: Error, failed to delete instance db: Error waiting for Delete Instance: 

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Checklist

I applicable, I acknowledge that I have:

• Read the contributing guide
• Ran terraform fmt on all modified files
• Regenerated the relevant README.md files using tools/tfdoc.py
• Made sure all relevant tests pass