[CrOS Cellular] Fix esim policy login metrics test

This CL enabled the eSIM policy flag in esim policy login metrics unit
tests and fix the histogram expected number since enabling the flag will
also trigger the record of metrics BlockNonManagedCellularHistogram in
managed network configuration handler[1]. Otherwise, enabling the ESim
Policy flag will fail the test.

[1]:https://source.chromium.org/chromium/chromium/src/+/main:chromeos/
network/managed_network_configuration_handler_impl.cc;l=705

Bug: b/207589472
Change-Id: I0447c48eee22750b9897fb5993211c7fb3928d45
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3414231


Reviewed-by: Azeem Arshad <azeemarshad@chromium.org>
Commit-Queue: Jason Zhang <jiajunz@google.com>
Cr-Commit-Position: refs/heads/main@{#963060}