Revert "CommunalBackup: Drop usages of runBlocking"

This reverts commit 99192e30.

Reason for revert: Causes crash on backup - when device is signed in and
online. Needs new API to handle dagger injection in backupAgent.
Bug: 434898486
Change-Id: I1e4a0923ade8555bcb7086fee7e3505aaa3ff2fc