Fix clippy

crates/weaver_diff/src/lib.rs

@@ -10,6 +10,7 @@ const RESET: &str = "\x1b[0m";
 
 /// Constructs a "diff" string of the original vs. updated.
 /// Will create colorized (ANSI) output w/ `+` representing additions and `-` representing removals.
+#[must_use]
 pub fn diff_output(original: &str, updated: &str) -> String {
     let mut result = String::new();
     let diff = TextDiff::from_lines(original, updated);