(aws-cdk-lib/aws_ec2): (Can't create Internet Gateway without public subnets)

### Describe the bug

I specified "create InternetGateway" prop true and "subnetConfiguration" as "PRIVATE_ISOLATED". But It doesn't make Internet Gateway. I Use Internet Gateway only for Cloud front VPC origin.

```
new _Vpc(this, 'Vpc', {
ipAddresses: IpAddresses.cidr('10.0.0.0/16'),
availabilityZones: ["ap-northeast-1a", "ap-northeast-1c"],
ipProtocol: IpProtocol.IPV4_ONLY,
createInternetGateway: true,
subnetConfiguration: [
{
cidrMask: 24,
name: 'SubnetA',
subnetType: SubnetType.PRIVATE_ISOLATED
},
{
cidrMask: 24,
name: 'SubnetB',
subnetType: SubnetType.PRIVATE_ISOLATED
},
{
cidrMask: 24,
name: 'SubnetC',
subnetType: SubnetType.PRIVATE_ISOLATED
},
{
cidrMask: 24,
name: 'SubnetD',
subnetType: SubnetType.PRIVATE_ISOLATED
},
]
});
```

### Regression Issue

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

### Last Known Working CDK Version

_No response_

### Expected Behavior

It makes Internet Gateway and Private Subnets

### Current Behavior

It doesn't makes Internet Gateway

### Reproduction Steps

```
new _Vpc(this, 'Vpc', {
ipAddresses: IpAddresses.cidr('10.0.0.0/16'),
availabilityZones: ["ap-northeast-1a", "ap-northeast-1c"],
ipProtocol: IpProtocol.IPV4_ONLY,
createInternetGateway: true,
subnetConfiguration: [
{
cidrMask: 24,
name: 'SubnetA',
subnetType: SubnetType.PRIVATE_ISOLATED
},
{
cidrMask: 24,
name: 'SubnetB',
subnetType: SubnetType.PRIVATE_ISOLATED
},
{
cidrMask: 24,
name: 'SubnetC',
subnetType: SubnetType.PRIVATE_ISOLATED
},
{
cidrMask: 24,
name: 'SubnetD',
subnetType: SubnetType.PRIVATE_ISOLATED
},
]
});
```

### Possible Solution

Remove the "allowOutbound" condition from the if statement in the process of creating an "Internet Gateway". However, I think it will have a big impact.

/packages/aws-cdk-lib/aws-ec2/lib/vpc.ts line 1614:1629
```
const createInternetGateway = props.createInternetGateway ?? true;
const allowOutbound = this.subnetConfiguration.filter(
subnet => (subnet.subnetType !== SubnetType.PRIVATE_ISOLATED && subnet.subnetType !== SubnetType.ISOLATED && !subnet.reserved)).length > 0;

// Create an Internet Gateway and attach it if necessary
if (allowOutbound && createInternetGateway) {
const igw = new CfnInternetGateway(this, 'IGW', {
});

this.internetGatewayId = igw.ref;

this._internetConnectivityEstablished.add(igw);
const att = new CfnVPCGatewayAttachment(this, 'VPCGW', {
internetGatewayId: igw.ref,
vpcId: this.resource.ref,
});
```

### Additional Information/Context

_No response_

### CDK CLI Version

2.1006.0

### Framework Version

_No response_

### Node.js Version

v23.10.0

### OS

Mac OS

### Language

TypeScript

### Language Version

_No response_

### Other information

_No response_

Start at packages/aws-cdk-lib/aws-ec2/lib/vpc.ts lines 1614-1629 and reproduce the supplied TypeScript VPC configuration with CDK synthesis. Trace how createInternetGateway and PRIVATE_ISOLATED subnet settings affect resource creation; done means the synthesized VPC includes an Internet Gateway attachment alongside the isolated subnets when requested.

Written by the indexing model from the issue text.