Default update notification color overrides admin color schemes

[celloexpressions]

The update notification bubbles in the admin menu display the default orange background color with every admin color scheme in 3.9.

The issue is that the selector for the default styles is #adminmenu span.update-plugins, while the color schemes use #adminmenu .update-plugins. While neither selector changed in 3.9, the styles did some. This is most likely a bug from the colors.css merge.

Best solution is probably to drop the span from the default styles, although that could cause breakage somewhere I'm missing. Alternatively, adding the span to the color schemes also resolves the issue, although that means regenerating all of the color schemes in what should probably be in a point release.

[nacin]

Looks good, Nick.

[helen]

I also prefer to simplify selectors where we can, and in testing didn't find any breakage. Rolling with the first patch.

[helen]

[28177] for trunk missed the ticket.

[nacin]

In 28204:

Simplify the admin menu notification selector so color schemes don't get stomped.

Merges [28177] to the 3.9 branch.

props celloexpressions.
fixes #27920.