Fix `TestAccECSClusterCapacityProviders_destroy` acceptance test

[ewbankkit]

The TestAccECSClusterCapacityProviders_destroy acceptance test is failing:

=== CONT  TestAccECSClusterCapacityProviders_destroy
    cluster_capacity_providers_test.go:120: Step 1/2 error: Check failed: Check 2/2 error: RegisteredContainerInstancesCount = 0, want 2
--- FAIL: TestAccECSClusterCapacityProviders_destroy (139.58s)

[github-actions[bot]]

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