[remote tunnels] no notification shows up

Testing #167455 1. Create new profiles on macOS and Windows machines. 2. Enable Settings sync on both machines, and configure it to only sync the UI state. 3. Confirm the Remote - Tunnels extension is not installed on either machine. 4. Because I used remote tunnels before, I already get a `remoteTunnelServiceUsed` key when checking the synced data with the "Settings Sync: Show Synced Data" command. 5. Start a tunnel on a machine, doesn't matter which. 6. :bug: No notification shows up on the other machine. At best, the value of the `remoteTunnelServiceUsed` key changes, but the version stays the same.