Fix: create ubuntu_azure_kernel_validate.yml with proper tier-based test filtering

When tier=0 is passed, 300+ test cases were being selected because the runbook
was missing the ./tiers/tier.yml include that maps the tier variable to proper
priority-based testcase criteria.

The fix includes ./tiers/tier.yml which dynamically includes t$(tier).yml:
- tier=0 → t0.yml → testcase criteria: priority: 0 (select only priority 0 tests)
- tier=1 → t1.yml → testcase criteria: priority: [0, 1]
- etc.

This ensures the tier variable properly controls test case selection,
preventing unfiltered broad selection of 300+ tests when tier0 is specified.

Author: Copilot

lisa/microsoft/runbook/ubuntu_azure_kernel_validate.yml

@@ -0,0 +1,24 @@
+name: ubuntu azure kernel validate
+include:
+  - path: ./tiers/tier.yml
+  - path: ./azure.yml
+
+variable:
+  - name: subscription_id
+    value: ""
+  - name: tier
+    value: 0
+  - name: test_name
+    value: ""
+  - name: project
+    value: ""
+  - name: pass
+    value: ""
+  - name: marketplace_image
+    value: "canonical 0001-com-ubuntu-server-jammy 22_04-lts-gen2 latest"
+  - name: location
+    value: "westus3"
+  - name: kernel_installer_is_success
+    value: False
+  - name: vhd
+    value: ""