Sensitive state is shared between tests

[obulat]

Description

In the Playwright tests, sometimes tests fetch sensitive data even if no features are set for them. No cookies are set when we do not alter any feature in preparePageForTests, so it seems that the tests are reading the cookie from another test.

Issue based on the comment

I don't know how, but it seems that the sensitive tests are changing the state for other tests, and make them add mature=true to requests. To prevent that, we always set fetch_sensitive to false if no features are passed here.

Originally posted by @obulat in #4222 (comment)

[obulat]

I think I found the reason for this issue and added a fix in #4231: the fetch_sensitive should be saved in the sessionFeatures cookie, not in the features cookie where the preparePageForTests was saving it.