Enable no mentions in commits of triagebot (rust-lang#14576)

This PR enables the no-mentions in commits handler in triagebot.

Documentation pending at
rust-lang/rust-forge#827

Original motivation in rust-lang#137990.

changelog: add `[no-mentions]` in `triagebot.toml`

Author: flip1995

triagebot.toml

@@ -13,6 +13,9 @@ allow-unauthenticated = [
 
 [canonicalize-issue-links]
 
+# Prevents mentions in commits to avoid users being spammed
+[no-mentions]
+
 # Have rustbot inform users about the *No Merge Policy*
 [no-merges]
 exclude_titles = ["Rustup"] # exclude syncs from rust-lang/rust