Fix validation task (matrix_postmoogle_ -> matrix_bot_postmoogle_)

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/3698

roles/custom/matrix_playbook_migration/tasks/validate_config.yml

@@ -227,7 +227,7 @@
   block:
     - ansible.builtin.set_fact:
         matrix_playbook_migration_postmoogle_migration_vars: |-
-          {{ vars | dict2items | selectattr('key', 'match', 'matrix_postmoogle_.*') | list | items2dict }}
+          {{ vars | dict2items | selectattr('key', 'match', 'matrix_bot_postmoogle_.*') | list | items2dict }}
 
     - name: (Deprecation) Catch and report matrix_bot_postmoogle variables
       ansible.builtin.fail: