Bump dart from `720e088` to `3e60b8f` in /auto_submit (#2336)

Bumps dart from `720e088` to `3e60b8f`.

---
updated-dependencies:
- dependency-name: dart
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
diff --git a/auto_submit/Dockerfile b/auto_submit/Dockerfile
index 76e25b8..f001447 100644
--- a/auto_submit/Dockerfile
+++ b/auto_submit/Dockerfile
@@ -4,7 +4,7 @@
 
 
 # Dart Docker official images can be found here: https://hub.docker.com/_/dart
-FROM dart:beta@sha256:720e088ddac7cc033117e20578133e01d70183b43114889abc6fb4485b05b089
+FROM dart:beta@sha256:3e60b8fa94aeeb76be28921eaaf46879786d2f3093e387fd3686d5f744f5f063
 
 WORKDIR /app