##### SUMMARY

A malformed list item in an included task file yields a cryptic message

##### ISSUE TYPE
- Bug Report

##### COMPONENT NAME

lib/ansible/cli/scripts/ansible_cli_stub.py

##### ANSIBLE VERSION

Confirmed as of c888035e
```
ansible 2.10.0.dev0
  config file = None
  configured module search path = ['/usr/share/ansible/plugins/modules']
  ansible python module location = /proj/ansible/ansible/venv/lib/python3.7/site-packages/ansible_base-2.10.0.dev0-py3.7.egg/ansible
  executable location = /proj/ansible/ansible/venv/bin/ansible
  python version = 3.7.7 (default, Mar 11 2020, 11:44:20) [GCC 9.2.1 20191008]
```

##### CONFIGURATION

##### OS / ENVIRONMENT

##### STEPS TO REPRODUCE

* bug.yml
```yaml
---
- oops
```
* pb.yml
```yaml
- hosts: all
  gather_facts: no
  tasks:
  - include_tasks: bug.yml
```

##### EXPECTED RESULTS

```console
$ ansible-playbook -i localhost, -c local pb.yml
ERROR! Traceback (most recent call last):
  File "/proj/ansible/ansible/lib/ansible/playbook/block.py", line 130, in _load_block
    use_handlers=self._use_handlers,
  File "/proj/ansible/ansible/lib/ansible/playbook/helpers.py", line 106, in load_list_of_tasks
    raise AnsibleAssertionError('The ds (%s) should be a dict but was a %s' % (ds, type(ds)))
ansible.errors.AnsibleAssertionError: The ds (['oops']) should be a dict but was a <class 'list'>
```
or something similar, because just _eating_ the `AnsibleParserError` makes tracking down the erroneous list item harder than necessary

##### ACTUAL RESULTS

```console
$ ansible-playbook -i localhost, -c local -vvvvvvvvv pb.yml
ansible-playbook 2.10.0.dev0
  config file = None
  configured module search path = ['/usr/share/ansible/plugins/modules']
  ansible python module location = /proj/ansible/ansible/lib/ansible
  executable location = /proj/ansible/ansible/venv/bin/ansible-playbook
  python version = 3.7.7 (default, Mar 11 2020, 11:44:20) [GCC 9.2.1 20191008]
No config file found; using defaults
setting up inventory plugins
Set default localhost to localhost
Parsed localhost, inventory source with host_list plugin
statically imported: /proj/ansible/ansible/bug.yml
ERROR! A malformed block was encountered while loading a block
```
and the same outcome when run with `ANSIBLE_DEBUG=1` which was especially surprising

```console
$ ANSIBLE_DEBUG=1 ansible-playbook -i localhost, -c local -vvvvvvvvv pb.yml
## snip
 22539 1585707905.71204: Loading BecomeModule 'sudo' from /proj/ansible/ansible/lib/ansible/plugins/become/sudo.py (found_in_cache=False, class_only=True)
 22539 1585707905.71232: Loading data from /proj/ansible/ansible/bug0.yml
 22539 1585707905.71591: in VariableManager get_vars()
 22539 1585707905.71621: done with get_vars()
 22539 1585707905.71634: Loading data from /proj/ansible/ansible/bug00.yml
statically imported: /proj/ansible/ansible/bug.yml
 22539 1585707905.71686: RUNNING CLEANUP
ERROR! A malformed block was encountered while loading a block
```
''' internal safeguards tripped, something happened in the code that should never happen '''
    pass
class AnsibleRuntimeError(AnsibleError):
    ''' ansible had a problem while running a playbook '''
    pass
class AnsibleModuleError(AnsibleRuntimeError):
    ''' a module failed somehow '''
    pass
class AnsibleConnectionFailure(AnsibleRuntimeError):
    ''' the transport / connection_plugin had a fatal error '''
    pass
class AnsibleAuthenticationFailure(AnsibleConnectionFailure):
    '''invalid username/password/key'''
    pass
class AnsibleCallbackError(AnsibleRuntimeError):
    ''' a callback failure '''
    pass
class AnsibleTemplateError(AnsibleRuntimeError):
    '''A template related error'''
    pass
class AnsibleFilterError(AnsibleTemplateError):
    ''' a templating failure '''
    pass
class AnsibleLookupError(AnsibleTemplateError):
    ''' a lookup failure '''
    pass
class AnsibleUndefinedVariable(AnsibleTemplateError):
    ''' a templating failure '''
    pass
class AnsibleFileNotFound(AnsibleRuntimeError):