docs(guide): Switch build-perf note from italics to bold

Author: epage

src/doc/src/guide/build-performance.md

@@ -122,7 +122,7 @@ Recommendation: Periodically review unused dependencies for removal using third-
 When changing code,
 it can be easy to miss that a dependency is no longer used and can be removed.
 
-> *Note:* native support for this in Cargo is being tracked in [#15813](https://github.com/rust-lang/cargo/issues/15813).
+> **Note:** native support for this in Cargo is being tracked in [#15813](https://github.com/rust-lang/cargo/issues/15813).
 
 Trade-offs:
 - ✅ Faster full build and link times