Bump dart from `65138b3` to `9fa6436` in /app_dart (#2270)

diff --git a/app_dart/Dockerfile b/app_dart/Dockerfile
index bce6c01..7b836dd 100644
--- a/app_dart/Dockerfile
+++ b/app_dart/Dockerfile
@@ -4,7 +4,7 @@
 
 
 # Dart Docker official images can be found here: https://hub.docker.com/_/dart
-FROM dart:beta@sha256:65138b3cbb561d2c9f7b2e6bf71454c10da097a61dc5e56d30a21bda22c34adc
+FROM dart:beta@sha256:9fa643606ff56e8837b342f4300e360267de82a0a6cc5e5ed265120aa1a5aa30
 
 WORKDIR /app