Fail when attempting to modify unmodifiable target group parameters (#33246)

* Fail when attempting to modify unmodifiable target group parameters

As you can't modify Port, Protocol or VPC id for a target group, fail
when this happens rather than pretending to do it.

One could argue that the target group could be recreated rather than
failing, but this has massive knock on implications to other resources
that depend on the TG (all ASGs would need to be updated, the ELB
listener would need to be updated, etc)

* Use `.get()` instead of direct dictionary access

lib/ansible/modules/cloud/amazon/elb_target_group.py

@@ -384,6 +384,11 @@ def create_or_update_target_group(connection, module):
     tg = get_target_group(connection, module)
 
     if tg:
+        diffs = [param for param in ('Port', 'Protocol', 'VpcId')
+                 if tg.get(param) != params.get(param)]
+        if diffs:
+            module.fail_json(msg="Cannot modify %s parameter(s) for a target group" %
+                             ", ".join(diffs))
         # Target group exists so check health check parameters match what has been passed
         health_check_params = dict()