(maint) Pin gha acceptance workflow to nested_vms@v1

I pulled out the action from kvm_automation_tooling into its own
nested_vms repo to isolate it. This switches acceptance to use
nested_vms@v1, which in turn uses kvm_automation_tooling@v1, so the
workflow is no longer tied to latest main from kvm_automation_tooling
and will only update when releases bump the floating v1 tags.

Author: jpartlow

.github/workflows/acceptance.yaml

@@ -69,7 +69,7 @@ jobs:
         with:
           fetch-depth: 0
       - id: vm-cluster
-        uses: jpartlow/kvm_automation_tooling@main
+        uses: jpartlow/nested_vms@v1
         with:
           os: ${{ matrix.os[0] }}
           os-version: ${{ matrix.os[1] }}