Move post_validate for tasks after checking for an include

Simplifies logic and prevents us from accidentally post_validating
an include that would otherwise be skipped due to tags causing a
problem because of potentially missing variables.

Fixes #12793

lib/ansible/plugins/strategy/__init__.py

@@ -401,6 +401,7 @@ class StrategyBase:
 
         try:
             data = self._loader.load_from_file(included_file._filename)
+            self._tqm.send_callback('v2_playbook_on_include', included_file)
             if data is None:
                 return []
         except AnsibleError as e: