Runtime update integration test

[ondratra]

During runtime upgrade proposals PR review https://github.com/Joystream/joystream/pull/3339 , I've noticed that there is a flow updateRuntime.ts in integration tests that doesn't seem to be called from any scenario, thus not used.

Investigate why it's not used (anymore?), either call it in one of the existing scenarios, create a new scenario or delete it if it's not useful anymore. Plus, consider adding a test for https://github.com/Joystream/joystream/pull/3339/files behavior and assess other on-runtime-update logic that could be tested as well.

┆Issue is synchronized with this Asana task by Unito