fix border color of feed/list embeds (#9021)

src/components/Post/Embed/FeedEmbed.tsx

···
   return (
     <FeedCard.Link
       view={embed.view}
-      style={[a.border, t.atoms.border_contrast_medium, a.p_md, a.rounded_sm]}>
+      style={[a.border, t.atoms.border_contrast_low, a.p_md, a.rounded_sm]}>
       <FeedCard.Outer>
         <FeedCard.Header>
           <FeedCard.Avatar src={embed.view.avatar} />

src/components/Post/Embed/ListEmbed.tsx

···
   return (
     <ListCard.Default
       view={embed.view}
-      style={[a.border, t.atoms.border_contrast_medium, a.p_md, a.rounded_sm]}
+      style={[a.border, t.atoms.border_contrast_low, a.p_md, a.rounded_sm]}
     />
   )
 }