fix: retain header and divider delimiter lengths when updating tests

This helps to prevent visual bloat in diffs when updating tests where the delimiter is not 80 chars long

cli/src/tests/corpus_test.rs

@@ -502,6 +502,7 @@ fn flatten_tests(test: TestEntry) -> Vec<FlattenedTest> {
                 input,
                 output,
                 has_fields,
+                ..
             } => {
                 if !prefix.is_empty() {
                     name.insert_str(0, " - ");