[fenix] For https://github.com/mozilla-mobile/fenix/issues/21887 - Update Home background color to LightGrey20

app/src/main/res/values/colors.xml

@@ -8,7 +8,7 @@
     <color name="secondary_text_light_theme">@color/photonGrey50</color>
     <color name="contrast_text_light_theme">@color/primary_text_dark_theme</color>
     <color name="caption_text_light_theme">@color/photonLightGrey90</color>
-    <color name="foundation_light_theme">@color/photonLightGrey10</color>
+    <color name="foundation_light_theme">@color/photonLightGrey20</color>
     <color name="inset_light_theme">@color/photonLightGrey30</color>
     <color name="above_light_theme">#FFF</color>
     <color name="accent_light_theme">@color/photonInk20</color>