Bump dart from `4c77cf9` to `86d317e` in /auto_submit (#2457)

Bumps dart from `4c77cf9` to `86d317e`.

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

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 4123478..a986fcd 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@sha256:4c77cf9c98c527de9df411da60c0f85195dfed20d48e19885ff69f2bd9a5ebb0
+FROM dart:beta@sha256:86d317e7e92835424db0263cd0cef52c7317aac51925846ead49178b7108189a
 
 WORKDIR /app