Fix ScanManagerTest#testFilteredScanTimeout

This change fixes test flakiness by changing the test to use
the TestLooper and assure MSG_SCAN_TIMEOUT is handled before test
assertions. Currently the test is using Thread.sleep which is causing
flakiness.

Bug: 324798161
Test: atest BluetoothInstrumentationTests
Flag: EXEMPT, test fix only
Change-Id: I85a3fe4a5f346c109a3f5ceee22910d086fb4b8b