Installed Languages list does not refresh on changes

### What Happened?

Due to the cached array here:
https://github.com/elementary/switchboard-plug-locale/blob/a2e23143c6b4104c88f170883588d090556e893d/src/Utils.vala#L31-L35

Whenever we use the plug to install/remove languages, the list of installed languages displayed in the sidebar is not updated to reflect the new reality.

### Steps to Reproduce

1. Install or remove a language
2. See that the change is not reflected in the sidebar
3. Restarting switchboard causes the state to update

### Expected Behavior

Languages that are removed should be removed from the list on successful removal
Languages that are installed should be added to the list on successful installation

### OS Version

6.x (Odin)

### Software Version

Latest release (I have run all updates)

### Log Output

_No response_

### Hardware Info

_No response_