Add rustbot to the blog repository

Author: Urgau

repos/rust-lang/blog.rust-lang.org.toml

@@ -2,7 +2,7 @@ org = "rust-lang"
 name = "blog.rust-lang.org"
 description = "Home of the Rust and Inside Rust blogs"
 homepage = "https://blog.rust-lang.org"
-bots = ["renovate"]
+bots = ["rustbot", "renovate"]
 
 [access.teams]
 inside-rust-reviewers = "write"