DynamoDB: Cannot perform more than one GSI creation or deletion in a single update

Hello,

I am receiving this error when trying to deploy using `sam deploy` to an existing environment but I keep receiving the following error:
```
DynamoDB: Cannot perform more than one GSI creation or deletion in a single update
```
I have two global secondary indexes on one table. The error seemed intuitive enough so I commented out all but one index at a time in my template file and it still throws the same error.

I then logged in to my AWS account and opted to deleted both indexes on the table and removed all mentions of GSIs from my template file and built it again but I still get the same error.

I don't know if I might have messed something up by removing the indexes directly from the AWS portal instead of using the SAM CLI? Could anyone help. Would greatly appreciate any pointers on how to get my builds running again.

### Version
SAM CLI, version 1.21.1