Fix ScanManagerTest#testFilteredScanTimeout

The test is flaky due to a race condition. Downgrade of scan mode is
expected to happen and the test checks this, however sometimes the check
takes place before downgrade is complete. Therefore, increasing waiting
time for downgrade. Change in AppScanStats.isScanningTooLong() is made
to avoid the corner case when the system executes all steps exactly in
time.

Bug: 297502921
Test: atest BluetoothInstrumentationTests
Change-Id: I507984b2c678cfdcf4541b527f6c316719fda07f