role fails in check mode

When trying out this role without any vars on a fresh debian 10 system I got this error:

```
FAILED! => {
"msg": "The task includes an option with an undefined variable. The error was: 'dict object' has no attribute 'stdout'\n\nThe error appears to be in '/home/peter/.ansible/roles/galaxyproject.postgresql/tasks/debian.yml': line 33, column 3, but may\nbe elsewhere in the file depending on the exact syntax problem.\n\nThe offending line appears to be:\n\n\n- name: Set version fact\n ^ here\n"
}
```

This is apparently because the task before, where the mentioned variable is to be registered, reports `"msg": "skipped, running in check mode"`