[Page header]Make header bottom border line only render for applicati…

…on header (#7973)

Signed-off-by: Zhongnan Su <[email protected]>

src/core/public/chrome/ui/header/header.scss

@@ -105,6 +105,6 @@
   width: 100%;
 }
 
-#globalHeaderBars {
+#globalHeaderBars:has(.primaryApplicationHeader) {
   border-bottom: 1px solid $euiColorLightShade;
 }