Roll Flutter from 587cf5fa715f to 78e3b93664c7 (23 revisions) (#6080)

diff --git a/.ci/flutter_master.version b/.ci/flutter_master.version
index 566ce01..b0a8d03 100644
--- a/.ci/flutter_master.version
+++ b/.ci/flutter_master.version
@@ -1 +1 @@
-587cf5fa715fffd95df9a224453f265482bb26f5
+78e3b93664c7784d806fe00080bd800f30cec662