Increase aws_polling values (#68)

Lately, our Windows images in AWS have been throwing a
`ResourceNotReady` error:

-
https://github.com/nv-gha-runners/vm-images/actions/runs/9697044936/job/26775090346#step:7:262
-
https://github.com/nv-gha-runners/vm-images/actions/runs/9697044936/job/26760297797#step:7:261

The link in the logs,
https://developer.hashicorp.com/packer/integrations/hashicorp/amazon#resourcenotready-error,
suggests that increasing the `aws_polling` values can resolve this.

Therefore, this PR increases the values of the `aws_polling` properties.

The default values are:

```hcl
aws_polling {
  delay_seconds = 15
  max_attempts = 40
}
```

source.pkr.hcl

@@ -74,7 +74,11 @@ source "amazon-ebs" "windows" {
   instance_type = local.instance_type
   region        = var.aws_region
 
-  skip_create_ami   = !var.upload_ami
+  skip_create_ami = !var.upload_ami
+  aws_polling {
+    delay_seconds = 25
+    max_attempts  = 60
+  }
   shutdown_behavior = "terminate"
   # the `user_data` file for AWS must be wrapped in a <powershell> tag
   user_data = <<-EOF