Fix CTS breakage for CtsDevicePolicyTestCases.

Ensure the idle check will be performed after bootup so that
the standby bucket could be refreshed immediately for the
protected packages.

Bug: 354599086
Test: atest CtsDevicePolicyTestCases:android.devicepolicy.cts.UserControlDisabledPackagesTest#setUserControlDisabledPackages_exemptFromStandbyBuckets
Change-Id: I6fb54a3bf035e06b8d3e4b2a7ec160cd830d4adc