### Summary

When using `difference` filter with element that have just case-difference in the value of the filter, only one is kept.

### Issue Type

Feature Request

### Component Name

filters

### Ansible Version

```console
$ ansible --version
ansible 2.9.10
  config file = None
  configured module search path = ['/home/user/.ansible/plugins/modules', '/usr/share/ansible/plugins/modules']
  ansible python module location = /usr/local/lib/python3.8/site-packages/ansible
  executable location = /usr/local/bin/ansible
  python version = 3.8.8 (default, Mar  4 2021, 21:24:42) [GCC 10.2.0]
```


### Configuration

```console
$ ansible-config dump --only-changed
```


### OS / Environment

RHEL 7

### Steps to Reproduce

```yaml
- hosts: localhost
  vars:
    list1:
      - a
      - A
      - b
      - B
    list2:
      - b
  tasks:
    - debug:
        msg: "{{ list1 | difference(list2) }}"
    - debug:
        msg: "{{ list1 | difference([]) }}"
```

```shell
ansible-playbook playbook.yml
```

### Expected Results

**All** the elements of `list1` that don’t exist in `list2` (as documented)

```
TASK [debug] ***********************
ok: [localhost] => {
    "msg": [
        "a",
        "A",
        "B"
    ]
}

TASK [debug] ***********************
ok: [localhost] => {
    "msg": [
        "a",
        "A",
        "b",
        "B"
    ]
}
```

### Actual Results

```console
TASK [debug] ***********************
ok: [localhost] => {
    "msg": [
        "a",
        "B"
    ]
}

TASK [debug] ***********************
ok: [localhost] => {
    "msg": [
        "a",
        "b"
    ]
}
```


### Code of Conduct

I agree to follow the Ansible Code of Conduct
''' Return a human readable string '''
    try:
        return formatters.bytes_to_human(size, isbits, unit)
    except TypeError as e:
        raise AnsibleFilterTypeError("human_readable() failed on bad input: %s" % to_native(e))
    except Exception:
        raise AnsibleFilterError("human_readable() can't interpret following string: %s" % size)
def human_to_bytes(size, default_unit=None, isbits=False):
    ''' Return bytes count from a human readable string '''
    try:
        return formatters.human_to_bytes(size, default_unit, isbits)
    except TypeError as e:
        raise AnsibleFilterTypeError("human_to_bytes() failed on bad input: %s" % to_native(e))
    except Exception:
        raise AnsibleFilterError("human_to_bytes() can't interpret following string: %s" % size)
def rekey_on_member(data, key, duplicates='error'):
    """
    Rekey a dict of dicts on another member
    May also create a dict from a list of dicts.
    duplicates can be one of ``error`` or ``overwrite`` to specify whether to error out if the key
    value would be duplicated or to overwrite previous entries if that's the case.
    """
    if duplicates not in ('error', 'overwrite'):