Use exhaustive match for assert

src/bootstrap/builder.rs

@@ -576,7 +576,7 @@ pub fn new(build: &Build) -> Builder<'_> {
                 Kind::Test | Kind::Doc | Kind::Build | Kind::Bench | Kind::Dist | Kind::Install => {
                     assert_eq!(this.top_stage, 2)
                 }
-                _ => {}
+                Kind::Check | Kind::Clippy | Kind::Fix | Kind::Run | Kind::Format => {}
             }
         }