Critical error logged on machines without bluetooth

## Prerequisites

- [x] I have searched open and closed issues for duplicates.

## Describe the bug

When I run wingpanel via the console, "CRITICAL" errors are logged. They look like this:

```
** (wingpanel:8112): CRITICAL **: 11:20:47.565: Manager.vala:58: Error calling StartServiceByName for org.bluez: GDBus.Error:org.freedesktop.DBus.Error.TimedOut: Failed to activate service 'org.bluez': timed out (service_start_timeout=25000ms)
```

### To Reproduce

Steps to reproduce the behavior:

1. On a machine that doesn't have bluetooth enabled, run `wingpanel` via the CLI.
2. Wait for 25s, see `CRITICAL` logs in the console

To run wingpanel from the CLI, do the following:

- Run `killall wingpanel` twice (this disables the auto-restart)
- Run `wingpanel`

### Expected behavior

This looks like it should be a debug log, not all machines do have bluetooth capabilities.

### Logs

```
** (wingpanel:8112): CRITICAL **: 11:20:47.565: Manager.vala:58: Error calling StartServiceByName for org.bluez: GDBus.Error:org.freedesktop.DBus.Error.TimedOut: Failed to activate service 'org.bluez': timed out (service_start_timeout=25000ms)
```

## Platform Information


- [ ] I'm using the latest version from git that I've manually compiled
- [x] I'm using the latest released stable version

## Additional Context

This is the line the log originates from: https://github.com/elementary/wingpanel-indicator-bluetooth/blob/e96dba1995d5a76b4b37b3219dc4189102e54fa7/src/Services/Manager.vala#L58