Merge branch 'boards-blank-state-size-fix' into 'master'

Fixed height of issue board blank state

## What does this MR do?

The height of the issue board blank state was causing some weird scrolling issues. This MR changes the height of the blank state.

See merge request !6960

app/assets/stylesheets/pages/boards.scss

-lex
 [v-cloak] {
   display: none;
 }
@@ -132,7 +131,7 @@ lex
 }
 
 .board-blank-state {
-  height: 100%;
+  height: calc(100% - 49px);
   padding: $gl-padding;
   background-color: #fff;
 }