fix margin in readonly mode (#8938)

* fix margin in readonly mode

when readonly mode is enabled with systemread or extended read
permissions, some fields are wrapped in a `pre` tag. By default `pre`
has a bigger margin-bottom . But in readonly mode we already have a
margin in a wrapping div which leads to unnecessary large space after
those fields.
So we should remove the margin-bottom for this

* fix style

war/src/main/scss/base/_style.scss

@@ -163,6 +163,10 @@ pre {
   }
 }
 
+pre.jenkins-readonly {
+  margin-bottom: 0 !important;
+}
+
 pre.console {
   overflow: auto;
 }