Temporarily use a non-default branch of cisagov/ansible-role-persist-…

…journald

This is being done for testing purposes and can be reverted once
cisagov/ansible-role-persist-journald#40 has been merged.

src/requirements.yml

@@ -30,6 +30,7 @@ roles:
     src: https://github.com/cisagov/ansible-role-nvme
   - name: persist_journald
     src: https://github.com/cisagov/ansible-role-persist-journald
+    version: improvement/use-drop-in
   - name: pip
     src: https://github.com/cisagov/ansible-role-pip
   - name: python