### Summary

One way this can happen is when Ansible runs as a non-priviledged user and ``/proc`` is mounted with ``hidepid=invisible``.
In this situation, ``ansible_service_mgr`` will be set to ``service`` as a fallback value.
Since the ``service`` module has no built-in support for ``runit``, it then fails to work correctly.

### Issue Type

Bug Report

### Component Name

module_utils

### Ansible Version

```console
$ ansible --version

ansible [core 2.11.0] 
  config file = None
  configured module search path = ['/home/user/.ansible/plugins/modules', '/usr/share/ansible/plugins/modules']
  ansible python module location = /usr/lib/python3.9/site-packages/ansible
  ansible collection location = /home/user/.ansible/collections:/usr/share/ansible/collections
  executable location = /usr/bin/ansible
  python version = 3.9.5 (default, May  5 2021, 14:50:57) [GCC 10.2.1 20201203]
  jinja version = 2.11.3
  libyaml = True
```


### Configuration

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


### OS / Environment

- Void Linux x86_64


### Steps to Reproduce

```
# Remount /proc so that normal user are not allowed to see process details of processes belonging to other users:
sudo mount -o remount,hidepid=2 /proc

# Check service_mgr fact gathered by Ansible:
ansible localhost -m setup|grep service_mgr
"ansible_service_mgr": "service",
```


### Expected Results

The expected output would be:
```
"ansible_service_mgr": "runit",
```

### Actual Results

The ``service`` fallback value is used:

```
"ansible_service_mgr": "service",
```


### Code of Conduct

- [X] I agree to follow the Ansible Code of Conduct
__test__ = True
    gather_subset = ['!all', 'ssh_pub_keys']
    valid_subsets = ['ssh_pub_keys']
    fact_namespace = 'ansible_ssh_pub_leys'
    collector_class = SshPubKeyFactCollector
class TestUserFactCollector(BaseFactsTest):
    __test__ = True
    gather_subset = ['!all', 'user']
    valid_subsets = ['user']
    fact_namespace = 'ansible_user'
    collector_class = UserFactCollector
class TestVirtualFacts(BaseFactsTest):
    __test__ = True
    gather_subset = ['!all', 'virtual']
    valid_subsets = ['virtual']
    fact_namespace = 'ansible_virtual'
    collector_class = VirtualCollector