[Feature Request]: Introduce a test case to ensure the `nested_roleAssignments.bicep` file references the correct `existing` resource

[AlexanderSehr]

Description

In some modules we seem to have incorrect existing resources in the nested_roleAssignments.bicep file which ultimately means the role assignments won't work.

To solve this, we should introduce a test that makes sure the referenced existing resource matches the module's resource type.