Fixed several issues with the confirmDismiss handling on the LeaveBehindItem demo. (#33080)

https://dart.googlesource.com/external/github.com/flutter/flutter/+/5ba0461b6d10e73763df28a86fc429f204781d39
diff --git a/commits.json b/commits.json
index b2f0364..f217cae 100644
--- a/commits.json
+++ b/commits.json
@@ -1,5 +1,5 @@
 {
   "external/github.com/flutter/engine":"301f560bd835e462134b491f1d5a74d21d03f3a8",
-  "external/github.com/flutter/flutter":"592f81e7c4eb31327b3cbf1e73d547587d6f7dea",
+  "external/github.com/flutter/flutter":"5ba0461b6d10e73763df28a86fc429f204781d39",
   "sdk":"4fe9951dcaf6a2dd947fc625035e5314395ee031"
 }
\ No newline at end of file