fix(hierarchical-grid): expander indicator not inheriting the background from the row. (#9487)

Co-authored-by: MPopov <[email protected]>
Co-authored-by: Simeon Simeonoff <[email protected]>

Author: 3 people

projects/igniteui-angular/src/lib/core/styles/components/grid/_grid-theme.scss

@@ -1210,6 +1210,7 @@
 
     %igx-grid__tr--inner {
         display: flex;
+        background: inherit;
     }
 
     %igx-grid__tr--add-animate {