### Summary

If a var is defined in the `vars:` of a block, and then redefined again in the `vars:` of an inner block, the outer value is still used.

`vars:` on a _task_ in the inner block work as expected.

### Issue Type

Bug Report

### Component Name

unknown

### Ansible Version

```console
$ ansible --version
ansible [core 2.12.0.dev0] (devel 1fc1ab89ae) last updated 2021/07/17 12:29:56 (GMT -400)
  config file = None
  configured module search path = ['/home/briantist/.ansible/plugins/modules', '/usr/share/ansible/plugins/modules']
  ansible python module location = /home/briantist/code/ansible/ansible.core/lib/ansible
  ansible collection location = /home/briantist/.ansible/collections:/usr/share/ansible/collections
  executable location = /home/briantist/code/ansible/ansible.core/bin/ansible
  python version = 3.6.9 (default, Jan 26 2021, 15:33:00) [GCC 8.4.0]
  jinja version = 3.0.1
  libyaml = True
```


### Configuration

```console
$ ansible-config dump --only-changed
CALLBACKS_ENABLED(env: ANSIBLE_CALLBACK_WHITELIST) = ['profile_tasks']
DEFAULT_FORKS(env: ANSIBLE_FORKS) = 30
INVENTORY_ENABLED(env: ANSIBLE_INVENTORY_ENABLED) = ['host_list', 'auto', 'ini', 'yaml', 'toml']
```


### OS / Environment

Ubuntu 18.04 on WSL2

### Steps to Reproduce

<!--- Paste example playbooks or commands between quotes below -->
```yaml
- name: outer
  vars:
    myvar: abc
  block:
    - debug:
        var: myvar

    - name: inner block
      vars:
        myvar: 123
      block:

        - debug:
            var: myvar

        - name: task
          vars:
            myvar: xyz
          debug:
            var: myvar
```

### Expected Results

inner block first `debug` result is `123`

### Actual Results

inner block first `debug` result is `abc`


### Code of Conduct

- [X] I agree to follow the Ansible Code of Conduct
_block = FieldAttribute(isa='list', default=list, inherit=False)
    _rescue = FieldAttribute(isa='list', default=list, inherit=False)
    _always = FieldAttribute(isa='list', default=list, inherit=False)
    
    _notify = FieldAttribute(isa='list')
    _delegate_to = FieldAttribute(isa='string')
    _delegate_facts = FieldAttribute(isa='bool')
    
    
    
    def __init__(self, play=None, parent_block=None, role=None, task_include=None, use_handlers=False, implicit=False):
        self._play = play
        self._role = role
        self._parent = None
        self._dep_chain = None
        self._use_handlers = use_handlers
        self._implicit = implicit
        if task_include:
            self._parent = task_include
        elif parent_block:
            self._parent = parent_block
        super(Block, self).__init__()
    def __repr__(self):
        return "BLOCK(uuid=%s)(id=%s)(parent=%s)" % (self._uuid, id(self), self._parent)
    def __eq__(self, other):