[AWS::RDS::DBProxyTargetGroup] - [BUG] - Drift detection fails with "dBProxyName must not be null"

### Name of the resource

AWS::RDS::DBProxyTargetGroup

### Resource Name

_No response_

### Issue Description

CloudFormation drift detection fails on AWS::RDS::DBProxyTargetGroup with a validation error indicating DBProxyName is null. This occurs even when the resource is correctly defined in the template and the stack deployed successfully. The error indicates that during the drift detection read operation, CloudFormation is passing a null DBProxyName to the RDS API rather than resolving the Ref to the proxy resource first.

The proxy resource itself (AWS::RDS::DBProxy) passes drift detection without issue — only the target group resource fails.

### Expected Behavior

Drift detection runs successfully on AWS::RDS::DBProxyTargetGroup. CloudFormation resolves the Ref on DBProxyName and calls DescribeDBProxyTargetGroups with the correct proxy name, returning a drift status of IN_SYNC or MODIFIED.

### Observed Behavior

Drift detection fails with:

The entire stack drift detection call exits with a non-zero error code, making it impossible to run drift detection on any stack containing this resource type.

### Test Cases

Deploy the following minimal CloudFormation template, then run aws cloudformation detect-stack-drift on the stack:

Expected result: drift detection completes and returns a status for MyProxyTargetGroup.

Observed result:
```
Failed to detect drift on resources [MyProxyTargetGroup]
1 validation error detected: Value null at 'dBProxyName' failed to satisfy constraint:
Member must not be null (Service: Rds, Status Code: 400)
```

### Other Details

Link to re:Post question about this issue https://repost.aws/questions/QUrE7SLmEzQAaYWi1oKDYUNA/cloud-formation-drift-detection-fails-for-aws-rds-db-proxy-target-group-with-d-b-proxy-name-must-not-be-null

Start by reproducing the issue with AWS::RDS::DBProxyTargetGroup and the aws cloudformation detect-stack-drift command described in the report. Trace the drift read operation for this resource and verify that it resolves DBProxyName before calling the RDS API; done means drift detection returns IN_SYNC or MODIFIED instead of the null-parameter validation error.

Written by the indexing model from the issue text.