aws-elasticloadbalancingv2-targets: LambdaTarget for external function throws error

### Describe the bug

When using the result of `Alias.fromAliasAttributes` as the argument of a `LambdaTarget`, it throws `ValidationError: Cannot modify permission to lambda function. Function is either imported or $LATEST version.` (whereas the similar `aws-apigateway` `LambdaIntegration` handles that input just fine). When using the (more verbose) `Function.fromFunctionAttributes` form (with `skipPermissions: true`), then the error thrown is `Error: [object Object] does not implement IDependable. Use "Dependable.implement()" to implement`, presumably because `grantInvoke` yields an undefined `policyDependable` with an external function/alias. https://github.com/aws/aws-cdk/blob/main/packages/aws-cdk-lib/aws-elasticloadbalancingv2-targets/lib/lambda-target.ts#L22

### Regression Issue

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

### Last Known Working CDK Library Version

_No response_

### Expected Behavior

Allow having a `LambdaTarget` from outside the stack.

### Current Behavior

Boom

### Reproduction Steps

```
// const aliasReference = Alias.fromAliasAttributes(stack, "alias", { aliasName, aliasVersion }); // would be preferred, simpler
const aliasReference = Function.fromFunctionAttributes(stack, "alias", { functionArn, skipPermissions: true });

// throws:
const tg = new ApplicationTargetGroup(stack, "tg", { targetGroupName, targets: [new LambdaTarget(aliasReference)] });
```

### Possible Solution

Don't try to grant automatically

### Additional Information/Context

_No response_

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

aws-cdk-lib@2.216.0

### AWS CDK CLI version

2.1029.2 (build fccc5f9)

### Node.js Version

v18.20.8

### OS

macOS 15.6.1

### Language

TypeScript

### Language Version

TypeScript (5.8.2)

### Other information

_No response_

Start in packages/aws-cdk-lib/aws-elasticloadbalancingv2-targets/lib/lambda-target.ts, then compare how the aws-apigateway LambdaIntegration handles imported aliases and external functions. Run the supplied TypeScript reproduction with Alias.fromAliasAttributes and Function.fromFunctionAttributes; done means LambdaTarget accepts an external function or alias without either permission-validation or IDependable errors.

Written by the indexing model from the issue text.