### Summary

Same issue reported here: https://github.com/ansible/ansible/issues/67266

Which was closed because it was "just a warning", but it is a bug because the warning occurs even when auto_silent is used. Just need to add an "if is_silent" check to this warning.

Ansible version: 2.9.11

### Issue Type

Bug Report

### Component Name

interpreter_discovery

### Ansible Version

```console
$ ansible --version
ansible 2.9.11
  config file = /etc/ansible/ansible.cfg
  configured module search path = ['/root/.ansible/plugins/modules', '/usr/share/ansible/plugins/modules']
  ansible python module location = /usr/lib/python3.6/site-packages/ansible
  executable location = /usr/bin/ansible
  python version = 3.6.8 (default, Dec  5 2019, 15:45:45) [GCC 8.3.1 20191121 (Red Hat 8.3.1-5)]
```


### Configuration

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


### OS / Environment

RHEL 8.2, ESXi 6.7 and 7.0 

### Steps to Reproduce

Run setup against an ESXi host with auto_silent interpreter; see warning.

### Expected Results

No warning about interpreter failure when silent mode is active.

### Actual Results

```console
Warning about no python interpreter when silent mode is active.
```


### Code of Conduct

I agree to follow the Ansible Code of Conduct
res = None
    platform_type = 'unknown'
    found_interpreters = [u'/usr/bin/python']  
    is_auto_legacy = discovery_mode.startswith('auto_legacy')
    is_silent = discovery_mode.endswith('_silent')
    try:
        platform_python_map = C.config.get_config_value('INTERPRETER_PYTHON_DISTRO_MAP', variables=task_vars)
        bootstrap_python_list = C.config.get_config_value('INTERPRETER_PYTHON_FALLBACK', variables=task_vars)
        display.vvv(msg=u"Attempting {0} interpreter discovery".format(interpreter_name), host=host)
        
        command_list = ["command -v '%s'" % py for py in bootstrap_python_list]
        shell_bootstrap = "echo PLATFORM; uname; echo FOUND; {0}; echo ENDFOUND".format('; '.join(command_list))
        
        res = action._low_level_execute_command(shell_bootstrap, sudoable=False)
        raw_stdout = res.get('stdout', u'')
        match = foundre.match(raw_stdout)
        if not match:
            display.debug(u'raw interpreter discovery output: {0}'.format(raw_stdout), host=host)
            raise ValueError('unexpected output from Python interpreter discovery')
        platform_type = match.groups()[0].lower().strip()
        found_interpreters = [interp.strip() for interp in match.groups()[1].splitlines() if interp.startswith('/')]
        display.debug(u"found interpreters: {0}".format(found_interpreters), host=host)
        if not found_interpreters:
            action._discovery_warnings.append(u'No python interpreters found for host {0} (tried {1})'.format(host, bootstrap_python_list))
            
            return u'/usr/bin/python'
        if platform_type != 'linux':
            raise NotImplementedError('unsupported platform for extended discovery: {0}'.format(to_native(platform_type)))
        platform_script = pkgutil.get_data('ansible.executor.discovery', 'python_target.py')