delete subnet should be idempotent (#35037)

lib/ansible/modules/cloud/azure/azure_rm_subnet.py

@@ -254,7 +254,7 @@ class AzureRMSubnet(AzureRMModuleBase):
                                                                                                  resource_guid=nsg.resource_guid)
 
                 self.results['state'] = self.create_or_update_subnet(subnet)
-            elif self.state == 'absent':
+            elif self.state == 'absent' and changed:
                 # delete subnet
                 self.delete_subnet()
                 # the delete does not actually return anything. if no exception, then we'll assume

test/integration/targets/azure_rm_subnet/tasks/main.yml

@@ -82,6 +82,17 @@
     virtual_network_name: My_Virtual_Network
     resource_group: "{{ resource_group }}"
 
+- name: Remove subnet (idempotent)
+  azure_rm_subnet:
+    state: absent
+    name: foobar
+    virtual_network_name: My_Virtual_Network
+    resource_group: "{{ resource_group }}"
+  register: output
+
+- assert:
+    that: not output.changed
+
 - name: Remove security group
   azure_rm_securitygroup:
     resource_group: "{{ resource_group }}"