[AVM Module Issue]: userAssignedManagedIdentities error out in avm/ptn/lz/sub-vending

### Check for previous/existing GitHub issues

- [x] I have checked for previous/existing GitHub issues

### Issue Type?

Bug

### Module Name

avm/ptn/lz/sub-vending

### (Optional) Module Version

0.5.2

### Description

When specifying userAssigedManagedIdentities property, it fails when assigning multiple roles to a single identity as follows:

``` bicep
...
userAssignedIdentityResourceGroupName: 'rg-${appName}-id-${environmentShort}-${location}'
userAssignedIdentitiesResourceGroupLockEnabled: false
userAssignedManagedIdentities: [
{
location: location
name: 'uami-${appName}-devops-${environmentShort}'
roleAssignments: [
{
definition: '/providers/Microsoft.Authorization/roleDefinitions/'
description: 'Role 1'
relativeScope: '' // subscription scope
}
{
definition: '/providers/Microsoft.Authorization/roleDefinitions/'
description: 'Role 2'
relativeScope: '' // subscription scope
}
]
}
]
```

The above code fails with the error: `Deployment template validation failed: 'The template reference 'createUserAssignedManagedIdentity[1]' is not valid: could not find template resource or resource copy with this name. Please see https://aka.ms/arm-function-reference for usage details.'."`

The code works if I only assign one role. It seems that the underlying code is iterating the managed identity with wrong index.

Thank you in advance for looking into it.

### (Optional) Correlation Id

_No response_