MqttConnectionSettings.CreateFromEnvVars does not work if the env var value contains '='

### This issue is for a: (mark with an `x`)
```
- [x] bug report -> please search issues before submitting
- [ ] feature request
- [ ] documentation issue or request
- [ ] regression (a behavior that used to work and stopped in a new release)
```

### Minimal steps to reproduce
Call MqttConnectionSettings.CreateFromEnvVars with a file containing a variable that contains an '=' in the value, such as MQTT_USERNAME=reg-cp-1/registrations/device-1/api-version=2023-12-01-preview

### Any log messages given by the failure
Silent failure.

### Expected/desired behavior
Environment variables with '=' in value are used.

### Language
C#

### OS and Version?
Any