Fix no member named 'unique' in 'std::shared_ptr<>'

With clang update, we got the following error:
frameworks/av/media/module/foundation/tests/AData_test.cpp:594:25:
error: no member named 'unique' in 'std::shared_ptr<a
ndroid::DerivedCounter>'
  594 |     EXPECT_TRUE(_shared.unique()); // now only _shared contains the object
      |                 ~~~~~~~ ^

Bug: 342023558
Test: build with clang update
Change-Id: I18f4814d3c288b6e34c78b57ea54ca51e85fc272