[Feature]: Get-AzResourceGroup should support multiple Tags

### Description of the new feature

Getting a single KV pair seems to work for Get-AzResourceGroup, but multiple tags seem to error.

The command `Get-AzResourceGroup -Tag @{"CostCenter" = "Platform" ; "Product" = "Stuff"}`

Currently gives error: `Get-AzResourceGroup: Invalid tag format. Expect @{tagName = $null} or @{tagName = "tagValue"}`

I noticed that Get-AzResource seems to work fine with multiple tags already.

### Proposed implementation details (optional)

_No response_

Start by reproducing the multiple-tag command shown in the issue, then compare Get-AzResourceGroup's tag handling with Get-AzResource, which already supports multiple tags. Locate the cmdlet implementation and its tests in the Azure PowerShell repository; done means the example accepts both tag pairs without the invalid-format error while existing single-tag behavior remains intact.

Written by the indexing model from the issue text.