ci: Use say_err instead of echo

We have a `say_err` function that echos to stderr, use it.

Author: tcharding

ci/run_task.sh

@@ -266,7 +266,7 @@ do_dup_deps() {
     duplicate_dependencies=$(eval "$tree_cmd")
 
     if [ "$duplicate_dependencies" -ne 0 ]; then
-        echo "Dependency tree is broken, contains duplicates"
+        say_err "Dependency tree is broken, contains duplicates"
         cargo tree  --target=all --all-features --duplicates
         exit 1
     fi