test: improve output format of issue10607a.go test

Change-Id: Iad5ff820a95f5082b75aa5260e40c33c7b0ecf22
Reviewed-on: https://go-review.googlesource.com/35990Reviewed-by: Russ Cox <rsc@golang.org>

test/fixedbugs/issue10607a.go

@@ -35,7 +35,7 @@ func main() {
 
 		d, err := s.Data()
 		if err != nil {
-			fmt.Fprintln(os.Stderr, "reading data of note section %d: %v", i, err)
+			fmt.Fprintf(os.Stderr, "reading data of note section %d: %v\n", i, err)
 			continue
 		}