fix(components/split-view): correct workspace background token in modern v2 (#3526)

[AB#3402770](https://dev.azure.com/blackbaud/Products/_boards/board/t/SKY%20UX%20Program/Stories?System.AssignedTo=%40me&workitem=3402770)

---------

Co-authored-by: Sandhya Adhirvuh <[email protected]>

Author: Blackbaud-SandhyaRajasabeson

apps/e2e/split-view-storybook/src/app/split-view/split-view.component.scss

@@ -9,12 +9,3 @@
   right: 0;
   bottom: 0;
 }
-
-sky-split-view-workspace-content {
-  background-color: yellow;
-}
-
-sky-split-view-workspace-footer {
-  background-color: green;
-  color: #fff;
-}

libs/components/split-view/src/lib/modules/split-view/split-view-workspace.component.scss

@@ -9,7 +9,7 @@
 .sky-split-view-workspace {
   background: var(
     --sky-override-split-view-workspace-background-color,
-    var(--sky-color-background-container)
+    var(--sky-color-background-container-base)
   );
   height: 100%;
   display: flex;