tests: Fix sha256 digest hex formatting for sha2 0.11 compat

The sha2 0.11 crate no longer implements LowerHex on the digest
output type. Format the hash by iterating over bytes instead, which
works with both 0.10 and 0.11.

Assisted-by: Claude Code (Opus 4.6)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: Xiaofeng Wang <henrywangxf@me.com>

Author: henrywang

src/lib.rs

@@ -679,7 +679,14 @@ mod tests {
             // testdata sha256sum are computed with a trailing \n
             sha256.update("\n");
             let filename = filename.trim_end_matches(".json");
-            let hash = format!("{:x}", sha256.finalize());
+            let digest = sha256.finalize();
+            let hash = digest
+                .iter()
+                .fold(String::new(), |mut s, b| {
+                    use std::fmt::Write;
+                    write!(s, "{b:02x}").unwrap();
+                    s
+                });
             assert_eq!(filename, hash);
             let json2: serde_json::Value = serde_json::from_slice(&enc)?;