[PSRule] Fix Rule Azure.VM.DiskCaching

[fabmas]

| RECOMMEND: | Check disk caching is configured correctly for the workload.

| REASON:
| - Path properties.storageProfile.osDisk.caching: Is set to 'ReadOnly'.

| HELP:
| - https://azure.github.io/PSRule.Rules.Azure/en/rules/Azure.VM.DiskCaching/

[microsoft-github-policy-service[bot]]

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[!TIP] For additional guidance on how to triage this issue/PR, see the BRM Issue Triage documentation.

[AlexanderSehr]

Hey @rahalan, I just migrated this issue over from CARML. Please take a look and triage if still relevant :)

[rahalan]

Already fixed with AVM