Add ansible.posix collection as a requirement, latest release.

Otherwise roles/custom/matrix-synapse/tasks/import_media_store.yml
won't run, taking the entire playbook with it.

requirements.yml

@@ -14,3 +14,6 @@
 
 - src: git+https://github.com/devture/com.devture.ansible.role.playbook_runtime_messages.git
   version: f1c78d4e85e875129790c58335d0e44385683f6b
+
+- src: git+https://github.com/ansible-collections/ansible.posix.git
+  version: 2d3f55caa73559736fdd378a05dd55bba4722fcc