…erence

Because there wasn't previously a handler for `onUpdate` events, an
empty object would be returned. When `installLatestAwsSdk` was changed
to `false`, this was an update. Typically, updates aren't an issue
because basically any other property being updated signifies a
replacement. `installLatestAwsSdk` is just a very unique case where it
doesn't (and where a user usually can't update it).

When the empty object is returned, this results in an update failure in
CloudFormation because the specific property isn't available.

Per the documentation, `onUpdate` is used when `onCreate` is not
defined. Since they're the same, we can just define `onUpdate`.

https://docs.aws.amazon.com/cdk/api/v2/docs/aws-cdk-lib.custom_resources.AwsCustomResource.html#oncreate