Story Block: (Android) video continues playing after closing Story

#### Issue

Following up on some feedback:

> On my Samsung S10e [Firefox v. 88.1.3, Chrome v. 90.0.4430.210] the video keeps playing even if I close the story (either by using the “Back” button native to the device or the “X” in the top right corner)

I don't have an Android device to test with, but I was _not_ able to reproduce the issue on latest iOS & Safari or Chrome.

#### Context

* Internal: p8oabR-FS-p2#comment-5319
* CC: @Tug

Start by reproducing the Story Block issue on Android, using both the device Back button and the X control to close the story while a video is playing. Done means the video stops playing after either close action, matching the reported behavior on iOS.

Written by the indexing model from the issue text.