/misc/watchdog-ok.png not used/displayed in the site status as it used to be in 6.x

There's #1086818: /misc/watchdog-ok.png not used/displayed in the site status as it used to be in 6.x filed for core. It was set to 8.x at some point (due to policy to first fix things in latest and then backport to previous versions), but #911054: Remove Garland from Core got in and it got switched back to 7.x. So, I'm filing this here so we don't miss fixing it for 8.x.

Issue summary from the respective core issue:

...as per title. I just noticed this now. I see that the table is rendered differently in 7.x and that there is now a "dedicated" <td> with a status-icon class, but that is only populated with icons for the parent <tr>s with classes warning or error, not the ones with ok class.