Skip changelog check for new services

[jonathan343]

Overview

The api-changelog-check.yml workflow currently detects when an AWS service model in codegen/aws-models is updated. Updated service models require a corresponding changelog entry describing the related changes (usually comes from the upstream service team). The workflow will fail if it doesn't see a new api-change entry under clients/aws-sdk-<service>/.changes/next-release/.

Problem

When a new service is added under codegen/aws-models, the workflow fails with an error similar to the one below:

- qbusiness (directory does not exist: clients/aws-sdk-qbusiness/.changes/next-release)

Our release infra automatically handles creating a new changelog entry for new services, so this is something we don't need to worry about here.

Solution

When a new service model is added, we'll skip the check since it's intended for updated service models only.

Testing

I pushed a new-service.json file and the workflow ran successfully (src):

Skipping new service 'new-service' (no package yet; changelog generated through release infra).
All modified models have corresponding changelog entries.

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