Disk Encryption Set with CMK fails with newer API versions

**Bicep version**
0.17.1

**Describe the bug**
See #6166

In my experience, this was not resolved. With the API version 2021-08-01 and using RBAC for KV access (haven't tried with access policies), it works.

However, with (at least some) later API versions, including the latest, it fails. Upon creation, the DES attempts to access the KV, which it can't because its system-assigned managed identity doesn't have permissions to the KV yet.

@brwilkinson Just pinging you here.

**To Reproduce**

Use the code from the issue above by Ben Wilkinson on Mar 10, 2022, but change the API version to a later version.

Begin with the reproduction code from issue #6166 and compare deployment behavior using API version 2021-08-01 against later versions, including the latest. Verify whether RBAC-based Key Vault access is configured and whether the Disk Encryption Set can access the vault during creation. Done means isolating the API-version-dependent failure and confirming the behavior with a minimal reproduction.

Written by the indexing model from the issue text.