Use say_err

We have an error function, use it.

This clears a shellcheck warning (unseen locally by myself) and puts the
error message below the ouput from `cargo tree` which is probably better
if its long.

ci/run_task.sh

@@ -256,9 +256,8 @@ do_dup_deps() {
     duplicate_dependencies=$(eval "$tree_cmd")
 
     if [ "$duplicate_dependencies" -ne 0 ]; then
-        echo "Dependency tree is broken, contains duplicates"
         cargo tree  --target=all --all-features --duplicates
-        exit 1
+        say_err "Dependency tree is broken, contains duplicates"
     fi
 
     set -o pipefail