Fix broken experiments table column shadow (#4099)

Author: julieg18

webview/src/experiments/components/table/body/branchDivider/BranchDivider.tsx

@@ -14,7 +14,7 @@ export const BranchDivider: React.FC<PropsWithChildren<BranchDividerProps>> = ({
   branch
 }) => (
   <thead data-testid="branch-name">
-    <tr>
+    <tr className={tablesStyles.experimentsTr}>
       <th className={tablesStyles.experimentsTd}>
         <div className={styles.branchName}>
           <Icon