luci-theme-material: add dropdown option hover styles

Subsequent commits will drop the JS based mouse following focus behavior,
so add appropriate replacement CSS hover styles.

Ref: #6903
Signed-off-by: Jo-Philipp Wich <jo@mein.io>

themes/luci-theme-material/htdocs/luci-static/material/cascade.css

@@ -1601,7 +1601,8 @@ body:not(.Interfaces) .cbi-rowstyle-2:first-child {
 	background: #b0d0f0;
 }
 
-.cbi-dropdown[open] > ul.dropdown > li.focus {
+.cbi-dropdown[open] > ul.dropdown > li.focus,
+.cbi-dropdown[open] > ul.dropdown > li:hover {
 	background: linear-gradient(90deg, #a3c2e8 0%, #84aad9 100%);
 }