aws_ecs: FargateTaskDefinition always adds default policy to execution role even when role is provided explicitly

### Describe the bug

I want to manage the task execution policy my self such as its attached policies. In particular, I would like to attach metadata to specific policies to add cfn_nag ignore statements.
This is not work if policies are attached behind the scenes.
In addition, the docs do that state this behaviour

### Regression Issue

- [ ] Select this option if this issue appears to be a regression.

### Last Known Working CDK Library Version

_No response_

### Expected Behavior

CDK does not attach any inline policies to the provided task execution IAM role.

### Current Behavior

Even though all required permissions are already attached to the custom task execution role, CDK attaches the default execution policy.

### Reproduction Steps

Create a FargateTaskDefinition with your custom execution role with custom inline permissions. Once deployed, look at the attached inline policies of that role. There will be the default execution policy be attached.

### Possible Solution

Do not attach the default policy

### Additional Information/Context

_No response_

### AWS CDK Library version (aws-cdk-lib)

/local/home/****/***** └── (empty)

### AWS CDK CLI version

2.1030.0 (build e46adaf)

### Node.js Version

v24.5.0

### OS

Linux CentOS

### Language

Python

### Language Version

Python 3.12

### Other information

_No response_

Start at the aws_ecs FargateTaskDefinition implementation and reproduce the issue with a custom execution role that already has inline permissions. Confirm the expected behavior by checking the synthesized or deployed role, and add or update coverage so a provided role receives no default execution policy.

Written by the indexing model from the issue text.