Variable only templates reporting missing property "stages"

[DigiBanks99]

If I use a variable-only template, I get a warning saying Missing property "stages". An example of a variable only template that produces this result:

variables:
  - group: 'my-variable-group'
  - name: 'myVariable'
    value: 'InitialValue'
``

Extensions version: `v1.208.0`

[jfranki]

I have this issue too. Extension version v1.247.2.

A more simple example:

variables:
  - name: dotnetSdkVersion
    value: 8.x

[winstliu]

Note to self. This is officially documented at https://learn.microsoft.com/en-us/azure/devops/pipelines/process/variables?view=azure-devops&tabs=yaml%2Cbatch#specify-variables and https://learn.microsoft.com/en-us/azure/devops/pipelines/process/templates?view=azure-devops&pivots=templates-extends#extend-from-a-template-and-use-an-include-template-with-variables. This will require a change on the ADO schema side.