Use relative uris for posts.

This tripped me up during testing. All links went to the production URL.
Makes more sense to make these relative I think!

src/layouts/BlogPosts.astro

@@ -62,7 +62,7 @@ const {
 			posts.map((post) => (
 				<PostCard
 					variant="large"
-					url={`${BLOG_URL}${post.url}`}
+					url={post.url}
 					title={post.data.title}
 					createdAt={post.data.createdAt.toISOString()}
 					image={post.data.image}