Resource type "Microsoft.RecoveryServices/vaults/backupFabrics@2021-06-01" does not have types available.

**Bicep version**
Bicep CLI version 0.4.613 (d826ce8411)

**Describe the bug**
When using existing resource declaration to address a backupFabric in a recoveryServices vault to deploy a protectionContainer, the following warning is given:
`Warning BCP081: Resource type "Microsoft.RecoveryServices/vaults/backupFabrics@2021-06-01" does not have types available.`

**To Reproduce**
```
resource recoveryServicesVault 'Microsoft.RecoveryServices/vaults@2021-06-01' existing = {
name: backupSettings.vaultName
}

resource backupFabric 'Microsoft.RecoveryServices/vaults/backupFabrics@2021-06-01' existing = {
name: 'Azure'
parent: recoveryServicesVault
}

resource protectionContainer 'Microsoft.RecoveryServices/vaults/backupFabrics/protectionContainers@2021-06-01' = {
name: 'storageContainer;Storage;${storageAccountResourceGroup};${storageAccountName}'
parent: backupFabric
properties: {
backupManagementType: 'AzureStorage'
containerType: 'StorageContainer'
sourceResourceId: storageAccount.id
}
}
```

Start by running the supplied Bicep reproduction with Bicep CLI 0.4.613 and inspect how the referenced Azure resource types are resolved. Done means the warning no longer appears for Microsoft.RecoveryServices/vaults/backupFabrics@2021-06-01 while the protectionContainer declaration remains valid.

Written by the indexing model from the issue text.