Roll Flutter Engine from 9196947bc687 to 6745955bb49e (2 revisions) (#144946)

https://github.com/flutter/engine/compare/9196947bc687...6745955bb49e

2024-03-11 zanderso@users.noreply.github.com Remove flaky check from observatory/tracing_test.dart (flutter/engine#51320)
2024-03-11 skia-flutter-autoroll@skia.org Roll Skia from cb30f40eea75 to f8d5ecc7841d (4 revisions) (flutter/engine#51321)

If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/flutter-engine-flutter-autoroll
Please CC rmistry@google.com,zra@google.com on the revert to ensure that a human
is aware of the problem.

To file a bug in Flutter: https://github.com/flutter/flutter/issues/new/choose

To report a problem with the AutoRoller itself, please file a bug:
https://issues.skia.org/issues/new?component=1389291&template=1850622

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+doc/main/autoroll/README.md

bin/internal/engine.version

-9196947bc68792e177a7c3cf03995f92f1165b8e
+6745955bb49e4e894a47cb48a19ffba504c69613