tests: fix flakky tests

Description

Fix following flakky tests:

> Task :app:testReleaseUnitTest
PlayStoreAuthenticatorTest > login_returnsSavedAuthWhenAvailable FAILED
    io.mockk.MockKException at PlayStoreAuthenticatorTest.kt:31
        Caused by: java.lang.ClassCastException at PlayStoreAuthenticatorTest.kt:31
PlayStoreAuthenticatorTest > login_usesAnonymousLoginWhenNoSavedAuth FAILED
    io.mockk.MockKException at PlayStoreAuthenticatorTest.kt:69
        Caused by: java.lang.ClassCastException at PlayStoreAuthenticatorTest.kt:69
PlayStoreAuthenticatorTest > login_fetchesUserProfileForGoogle FAILED
    io.mockk.MockKException at PlayStoreAuthenticatorTest.kt:108
        Caused by: java.lang.ClassCastException at PlayStoreAuthenticatorTest.kt:108

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