add inside-rust-reviewers as reviewers for inside-rust

Author: pietroalbini

.github/CODEOWNERS

@@ -1,4 +1,4 @@
 * @rust-lang/website
 posts/* @rust-lang/core
-posts/inside-rust/* @rust-lang/leads @rust-lang/core
+posts/inside-rust/* @rust-lang/inside-rust-reviewers @rust-lang/core
 .github/CODEOWNERS @rust-lang/core