cleanup: derive Default where possible

Not doing so triggers a clippy lint on Rust >= 1.91.

Part of #12013

src/builtins/block.rs

@@ -3,7 +3,7 @@
 // Implementation of the block builtin.
 use super::prelude::*;
 
-#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
+#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
 enum Scope {
     #[default]
     Unset,

src/highlight/highlight.rs

@@ -1213,9 +1213,8 @@ fn get_fallback(role: HighlightRole) -> HighlightRole {
 }
 
 /// Describes the role of a span of text.
-#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
+#[derive(Clone, Copy, Debug, Default, Eq, Hash, PartialEq)]
 #[repr(u8)]
-#[derive(Default)]
 pub enum HighlightRole {
     #[default]
     normal, // normal text