Topics in the spam view should not use the `bbp-lead-topic` background color

[netweb]

The spam view at ​https://wordpress.org/support/view/spam/ currently uses the bbp-lead-topic CSS class as the background colour for spammed topics

Via Slack here: ​https://wordpress.slack.com/archives/forums/p1473684980003792:

zoonini: hey peeps, anyone know the difference between the light pink and the orange ones in the spam queue?
zoonini: they both are author-flagged and marked as spam
sergey: @zoonini Looking at the HTML source, seems like the orange ones are initial topic posts, and light pink ones are replies.

Currently via https://meta.trac.wordpress.org/browser/sites/trunk/wordpress.org/public_html/wp-content/themes/pub/wporg-forums/style.css?marks=309-315#L309

#bbpress-forums ul.bbp-lead-topic li.bbp-body {
        border: 1px solid #ffe399;
}

#bbpress-forums ul.bbp-lead-topic li.bbp-body div.topic {
        background-color: #fff8e5;

It should inherit the background alternate colors from: ​https://plugins.trac.wordpress.org/browser/bbpress/trunk/templates/default/css/bbpress.css?marks=48-56#L48

#bbpress-forums .status-trash.even,
#bbpress-forums .status-spam.even {
        background-color: #fee;
}

#bbpress-forums .status-trash.odd,
#bbpress-forums .status-spam.odd {
        background-color: #fdd;
}

[coffee2code]

In 4070:

Forums Theme: Set background-color for spam, trash, and pending replies to supersede defaults.

Props SergeyBiryukov.
Fixes #2028.