Failing to attach ACR to AKS with az aks update

## Describe the bug

Recently ran into an issue where our Azure Pipelines were failing due to AKS not pulling contains from the ACR it's associated with.

Decided to check the service principal that is associated with the AKS using `az aks show --resource-group {rg-name} --name {aks-name} --query servicePrincipalProfile.clientId` followed by `az ad sp credential list --id "{id}" --query "[].endDate"` which said the expiration was in 2299 so it hasn't actually expired.

So I decided to try `az aks update -n {aks-name} -g {rg-name} --attach-acr {acr-name}` to make sure it was attached correctly, and received the error below.

This in a way verified the issue we are seeing with the AKS not pulling from the ACR because it too thinks the credentials are invalid.

**Command Name**
`az aks update`

**Errors:**
```
Operation failed with status: 'Bad Request'. Details: The credentials in ServicePrincipalProfile were invalid. Please see https://aka.ms/aks-sp-help for more details. (Details: adal: Refresh request failed. Status Code = '401'. Response body: {"error":"invalid_client","error_description":"AADSTS7000222: The provided client secret keys are expired. Visit the Azure Portal to create new keys for your app, or consider using certificate credentials for added security: https://docs.microsoft.com/azure/active-directory/develop/active-directory-certificate-credentials\r\nTrace ID: 4d883dc1-f690-4750-9a20-bb70a4086a00\r\nCorrelation ID: 6270a346-27ec-4a57-bfcb-05c2e30ed75b\r\nTimestamp: 2021-04-22 16:13:41Z","error_codes":[7000222],"timestamp":"2021-04-22 16:13:41Z","trace_id":"4d883dc1-f690-4750-9a20-bb70a4086a00","correlation_id":"6270a346-27ec-4a57-bfcb-05c2e30ed75b","error_uri":"https://login.microsoftonline.com/error?code=7000222"} Endpoint https://login.microsoftonline.com/79f4ee44-b070-4e6...
```

## To Reproduce:
Steps to reproduce the behavior. Note that argument values have been redacted, as they may contain sensitive information.

- `az aks update -n {} -g {} --attach-acr {}`

## Expected Behavior

AKS should update with the attached ACR.

## Environment Summary
```
Windows-10-10.0.19041-SP0
Python 3.6.8
Installer: MSI

azure-cli 2.22.1

```
## Additional Context