### 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
'''object comparison based on _uuid'''
        return self._uuid == other._uuid
    def __ne__(self, other):
        '''object comparison based on _uuid'''
        return self._uuid != other._uuid
    def get_vars(self):
        '''
        Blocks do not store variables directly, however they may be a member
        of a role or task include which does, so return those if present.
        '''
        all_vars = self.vars.copy()
        if self._parent:
            all_vars.update(self._parent.get_vars())
        return all_vars
    @staticmethod
    def load(data, play=None, parent_block=None, role=None, task_include=None, use_handlers=False, variable_manager=None, loader=None):
        implicit = not Block.is_block(data)
        b = Block(play=play, parent_block=parent_block, role=role, task_include=task_include, use_handlers=use_handlers, implicit=implicit)
        return b.load_data(data, variable_manager=variable_manager, loader=loader)
    @staticmethod
    def is_block(ds):
        is_block = False
        if isinstance(ds, dict):
            for attr in ('block', 'rescue', 'always'):
                if attr in ds:
                    is_block = True
                    break
        return is_block
    def preprocess_data(self, ds):