Fix subscription content-filtering flakiness

See the log below:
  
subscription content-filtering
    ✔ isContentFilteringEnabled
    ✔ no parameters (1002ms)
    ✔ single parameter (1001ms)
    ✔ multiple parameters (1002ms)
    ✔ setContentFilter (2003ms)
pure virtual method called
terminate called without an active exception
Aborted (core dumped)
Error: Process completed with exit code 134.