Update our preferences to account for new line height

Bugzilla bug 1872788 removed the line-height: 1.8em rule from the <label> and <description> elements. This had made some of our designs more compact. Most noticeable for the security settings:

But we also added our own line-height: 1.8 rule to our tor bridge preferences, which is now inconsistent (most noticeable under the bridge bot image):

/cc @donuts