ci: prevent cross-PR CI cancellation for mshv workflows

The existing concurrency configuration causes workflow runs for one Pull
Request to cancel in-progress runs for another Pull Request. When the
workflow is triggered by the `pull_request_target event`, `github.ref`
is always set to the base branch, regardless of which branch raised the
PR. This causes every new pull request to share the same concurrency key
and thus cancel the running CI of any other open pull request.

This commit updates the `concurrency.group` to use
`github.event.pull_request.number` for unique isolation when running on
PR, falling back to `github.ref` for non-PR push (e.g., merge group).

Signed-off-by: AASTHA RAWAT <aastharawat@microsoft.com>

.github/workflows/mshv-infra.yaml

@@ -38,7 +38,7 @@ on:
         description: 'Private IP of the VM'
         value: ${{ jobs.infra-setup.outputs.PRIVATE_IP }}
 concurrency:
-  group: ${{ github.workflow }}-${{ github.ref }}
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
   cancel-in-progress: true
 jobs:
   infra-setup: