tests: validate netplan API YAML instead of strict content (#5195)

Netplan API is used on Mantic and later which prevents cloud-init
from writing a header comment in /etc/netplan/50-cloud-init.yaml.

Only compare the loaded YAML dict of networking config instead of
the full content of the file before and after upgrade to assert
the equality of network config.

tests/integration_tests/test_networking.py

@@ -198,7 +198,10 @@ def test_netplan_rendering(
     }
     with session_cloud.launch(launch_kwargs=launch_kwargs) as client:
         result = client.execute("cat /etc/netplan/50-cloud-init.yaml")
-        assert result.stdout.startswith(EXPECTED_NETPLAN_HEADER)
+        if CURRENT_RELEASE < MANTIC:
+            assert result.stdout.startswith(EXPECTED_NETPLAN_HEADER)
+        else:
+            assert EXPECTED_NETPLAN_HEADER not in result.stdout
         assert expected == yaml.safe_load(result.stdout)
 
 

tests/integration_tests/test_upgrade.py

@@ -12,6 +12,7 @@
     CURRENT_RELEASE,
     FOCAL,
     IS_UBUNTU,
+    MANTIC,
     NOBLE,
 )
 from tests.integration_tests.util import verify_clean_log
@@ -154,7 +155,17 @@ def test_clean_boot_of_upgraded_package(session_cloud: IntegrationCloud):
                 values.pop("dhcp6")
             assert yaml.dump(pre_network) == yaml.dump(post_network)
         else:
-            assert pre_network == post_network
+            if CURRENT_RELEASE < MANTIC:
+                # Assert the full content is preserved including header comment
+                # since cloud-init writes the file directly and does not use
+                # netplan API to write 50-cloud-init.yaml.
+                assert pre_network == post_network
+            else:
+                # Mantic and later Netplan API is used and doesn't allow
+                # cloud-init to write header comments in network config
+                assert yaml.safe_load(pre_network) == yaml.safe_load(
+                    post_network
+                )
 
         # Calculate and log all the boot numbers
         pre_analyze_totals = [