### 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
self._dep_chain = data.get('dep_chain', None)
        
        role_data = data.get('role')
        if role_data:
            r = Role()
            r.deserialize(role_data)
            self._role = r
        parent_data = data.get('parent')
        if parent_data:
            parent_type = data.get('parent_type')
            if parent_type == 'Block':
                p = Block()
            elif parent_type == 'TaskInclude':
                p = TaskInclude()
            elif parent_type == 'HandlerTaskInclude':
                p = HandlerTaskInclude()
            p.deserialize(parent_data)
            self._parent = p
            self._dep_chain = self._parent.get_dep_chain()
    def set_loader(self, loader):
        self._loader = loader
        if self._parent:
            self._parent.set_loader(loader)
        elif self._role:
            self._role.set_loader(loader)
        dep_chain = self.get_dep_chain()
        if dep_chain:
            for dep in dep_chain:
                dep.set_loader(loader)
    def _get_parent_attribute(self, attr, extend=False, prepend=False):