Fix ScanManager#profileConnectionStateChanged_sendStartConnectionMessage

This fixes the previously flaky test by checking if the function
correctly calls ScanManager#handleConnectingState, which makes
ScanManger.mIsConnecting true.

Bug: 300012915
Test: atest BluetoothInstrumentationTests
Change-Id: I5538cc85d6a15040aca6d8b7254982ed6b18da0b