imac_active binary_sensor remains on after shutdown

**Device model, version and app version**

Model Name: iMac (24" Early 2009)
macOS Version: 10.15.3
App Version: 2021.6 (2021.158)
Safari Version: Version 13.0.5 (15608.5.11) but using Brave (Version 1.25.70 Chromium: 91.0.4472.77 (Official Build) (x86_64))

**Home Assistant Core Version**

core-2021.6.3

**Describe the bug**

binary_sensor.pierres_imac_active remains active when iMac is shutdown.

**To Reproduce**

Shutdown the iMac

**Expected behavior**

binary_sensor.pierres_imac_active should switch to 'off' when iMac is shutdown.

**Screenshots**

Screenshot taken on iPhone after iMac is shutdown.

**Additional context**

No source file or test is named. Reproduce with the macOS app on macOS 10.15.3, app version 2021.6, and Home Assistant Core 2021.6.3, then inspect how the iMac activity sensor is updated across shutdown; done means binary_sensor.pierres_imac_active changes to off after shutdown.

Written by the indexing model from the issue text.