Speculatively change IccCardProxyTest Mock Syntax

There is a WrongTypeOfReturnValue Exception thrown
by Mockito once in a while on IccCardProxyTest, which
seems to indicate a multithreading issue. These tests
use the same sort of syntax as other multithreaded
tests, and Mockito suggests using an alternate syntax
for reasons that I cannot understand. I cannot repro
the issue locally (ran > 1000 iterations), but perhaps
this will resolve the problem. It certainly isn't
making anything worse.

Bug: 70949390
Test: runtest -x ...IccCardProxyTest.java
Change-Id: I3d5cbaaf975da7557b5ea6ea8ebffd5d790ac247