Fix problem causing tasks to timeout. (#76028)

This is because the command was actually collecting logs continuously
from the device. Additionally idevicesyslog does not have a reboot
option.

Bug: https://github.com/flutter/flutter/issues/76027

dev/devicelab/lib/framework/adb.dart

@@ -793,7 +793,7 @@ class IosDevice extends Device {
 
   @override
   Future<void> reboot() {
-    return Process.run('idevicesyslog', <String>['reboot', '-u', deviceId]);
+    return Process.run('idevicediagnostics', <String>['restart', '-u', deviceId]);
   }
 }