Update PinnerService TEST_MAPPING

Ensure PinnerServiceTest runs in presubmit for changes to PinnerService.

Note: Configuring pre/postsubmit for FrameworksServicesTests for tests
in the top-level `com.android.server` package is awkward due to package
wildcards and TEST_MAPPING inheritance. A longer term solution would be
to migrate PinnerService into a more explicit sub-package, and/or break
its tests out into a separate test target.

Bug: 309853498
Test: presubmit
Change-Id: If60c9927e6db38dc96e6a2c765fee437b2f07605