verify_dns_name_resolution_after_upgrade - mark node dirty after OS u… (#4511)

* verify_dns_name_resolution_after_upgrade - mark node dirty after OS update

After OS upgrade sometimes kernel version may change. When LISA is used to validate a VM image with specific kernel version, changing the kernel will result in running tests with undesired kernel which should be avoided. Marking the node dirty after OS update to avoid such issues.

* move mark_dirty to after_case

---------

Co-authored-by: Srikanth Myakam <374767+SRIKKANTH@users.noreply.github.com>

Author: SRIKKANTH

lisa/microsoft/testsuites/core/dns.py

@@ -3,8 +3,10 @@
 from __future__ import annotations
 
 import re
+from typing import Any
 
 from lisa import (
+    Logger,
     Node,
     TestCaseMetadata,
     TestSuite,
@@ -39,6 +41,11 @@ class Dns(TestSuite):
         r"ModuleNotFoundError: No module named \'apt_inst\'", re.M
     )
 
+    def after_case(self, log: Logger, **kwargs: Any) -> None:
+        log.debug("after_case: mark node as dirty to avoid affecting other test cases")
+        node = kwargs["node"]
+        node.mark_dirty()
+
     @TestCaseMetadata(
         description="""
         This test case check DNS name resolution by ping bing.com.