Update New-AzGalleryImageVersion.md (#26259)

Wrong property was used to create from a VM

Author: lbouriez

src/Compute/Compute/help/New-AzGalleryImageVersion.md

@@ -38,8 +38,8 @@ $galleryName = "myGallery"
 $galleryImageDefinitionName = "myImage"
 $galleryImageVersionName = "1.0.0"
 $location = "eastus"
-$sourceImageId = "/subscriptions/00000000-0000-0000-0000-000000000000/resourceGroups/myVMRG/providers/Microsoft.Compute/virtualMachines/myVM"
-New-AzGalleryImageVersion -ResourceGroupName $rgName -GalleryName $galleryName -GalleryImageDefinitionName $galleryImageDefinitionName -Name $galleryImageVersionName -Location $location -SourceImageId $sourceImageId
+$sourceImageVMId = "/subscriptions/00000000-0000-0000-0000-000000000000/resourceGroups/myVMRG/providers/Microsoft.Compute/virtualMachines/myVM"
+New-AzGalleryImageVersion -ResourceGroupName $rgName -GalleryName $galleryName -GalleryImageDefinitionName $galleryImageDefinitionName -Name $galleryImageVersionName -Location $location -SourceImageVMId $sourceImageVMId
 ```
 
 Add a new image version from a virtual machine into the image definition.