Fix accidental HTML tag
Fix accidental HTML tag

The markdown parser was interpreting the `<something>` in `adjust_upvar_borrow_kind_for_<something>` as an HTML tag that was hidden in the rendered text. This minor edit fixes that.
rust-lang/rustc-dev-guide,rust-lang/rustc-dev-guide,rust-lang/rustc-dev-guide,rust-lang/rustc-dev-guide