fix(dashboards): Prevent Big Number rendering error if a description is present (#77313)

Another small edge case. During widget preview, the Big Number widget
has a min-height of 96px. If there's a widget description, this isn't
enough space to render the actual value, so the Big Number rendering
essentially fails.

I'm increasing its height to 120px, which is the minimum actual height
of the widget, as defined in the grid definition.

static/app/views/dashboards/widgetBuilder/buildSteps/visualizationStep.tsx

@@ -154,6 +154,7 @@ const VisualizationWrapper = styled('div')<{displayType: DisplayType}>`
   padding-right: ${space(2)};
   ${WidgetCardPanel} {
     height: initial;
+    min-height: 120px;
   }
   ${p =>
     p.displayType === DisplayType.TABLE &&