fix: Userpool does not exist

[ShadowCat567]

Description of changes

After the SDK V2->V3 migrations PR that affected auth, geo, and predictions was released, it was reported that running amplify push in some instances, after adding or updating something in the auth category, would show the error User pool client [clientId] does not exist..
This is caused by the migrated V3 clients consuming credentials that were being served to them using the V2 style and falling back to using the default profile.

V2 Style Credentials:
{
  accessKeyId: accessKeyId,
  secretAccessKey: secretAccessKey,
  region: region
}

V3 Style Credentials: 
{
  credentials: {
    accessKeyId: accessKeyId,
    secretAccessKey: secretAccessKey
  },
  region: region
}

Issue #, if available

#14260

Description of how you validated changes

Reproduced the issue and verified that the error no longer appeared when using an environment identical to the reproduction with the fix enabled.

Checklist

• PR description included
• yarn test passes
• Tests are changed or added
• Relevant documentation is changed or added (and PR referenced)
• New AWS SDK calls or CloudFormation actions have been added to relevant test and service IAM policies
• Pull request labels are added

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