refactor(ecs-patterns): organize tests (#29170)

### Issue # (if applicable)

part of #29041, #29039
continuation of #29153

Closes #<issue number here>.

### Reason for this change

tests in `packages/aws-cdk-lib/aws-ecs-patterns/test/ec2/l3s.test.ts` was disorganized.


### Description of changes

- No logical change.
- Organized tests in `packages/aws-cdk-lib/aws-ecs-patterns/test/ec2/l3s.test.ts` as below.

```ts
describe('ApplicationLoadBalancedEc2Service', () => {
...
})

describe('NetworkLoadBalancedEc2Service', () => {
...
})
```

- move tests of `ApplicationLoadBalancedFargateService`, `NetworkLoadBalancedFargateService` in `packages/aws-cdk-lib/aws-ecs-patterns/test/ec2/l3s.test.ts` to `packages/aws-cdk-lib/aws-ecs-patterns/test/fargate/load-balanced-fargate-service.test.ts`.



### Description of how you validated changes

Pass unit tests


### Checklist
- [x] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md)

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

packages/aws-cdk-lib/aws-ecs-patterns/test/ec2/l3s-v2.test.ts

@@ -22,7 +22,7 @@ import { NamespaceType } from '../../../aws-servicediscovery';
 import { Duration, Stack } from '../../../core';
 import { ApplicationMultipleTargetGroupsEc2Service, NetworkMultipleTargetGroupsEc2Service } from '../../lib';
 
-describe('When Application Load Balancer', () => {
+describe('ApplicationMultipleTargetGroupsEc2Service', () => {
   test('test ECS ALB construct with default settings', () => {
     // GIVEN
     const stack = new Stack();
@@ -893,7 +893,7 @@ describe('When Application Load Balancer', () => {
   });
 });
 
-describe('When Network Load Balancer', () => {
+describe('NetworkMultipleTargetGroupsEc2Service', () => {
   test('test ECS NLB construct with default settings', () => {
     // GIVEN
     const stack = new Stack();