Display proper error on group_vars syntax error
Display proper error on group_vars syntax error

This fix ensures a proper error is shown when a group_vars files cannot
be parsed correctly. Without this patch you get:

```
[dag@moria ansible.testing]$ ansible-playbook test132.yml
ERROR! Unexpected Exception: dictionary update sequence element #0 has length 1; 2 is required
to see the full traceback, use -vvv
```

With this patch you get:
```
[dag@moria ansible.testing]$ ansible-playbook test132.yml
ERROR! Problem parsing file '/home/dag/home-made/ansible.testing/group_vars/test135': line 1, column 1
```

This fixes #18843

thaim/ansible,thaim/ansible