Fix containerapp update using yml file

I think the upgrade to the new API version (Azure#31276) lead to `runningStatus` appearing as a field at the top level when the YAML file passed to `az containerapp update` is run through the deserialiser.

It then caused an error before the command was run:

```
(InvalidRequestContent) The request content was invalid and could not be deserialized: 'Could not find member 'runningStatus' on object of type 'ResourceDefinition'. Path 'runningStatus', line 1, position 224.'.
```

The fix is to add it to the existing list of readonly attributes to remove.

Author: mbarton

src/azure-cli/azure/cli/command_modules/containerapp/_utils.py

@@ -949,7 +949,8 @@ def _remove_readonly_attributes(containerapp_def):
         "latestRevisionFqdn",
         "customDomainVerificationId",
         "outboundIpAddresses",
-        "fqdn"
+        "fqdn",
+        "runningStatus"
     ]
 
     for unneeded_property in unneeded_properties: