Roll Flutter Engine from 5a924a9017d7 to 81b93fc4a2cc (2 revisions) (#135093)

https://github.com/flutter/engine/compare/5a924a9017d7...81b93fc4a2cc

2023-09-20 skia-flutter-autoroll@skia.org Roll Fuchsia Mac SDK from 06g6i7-5u8O-FOTSi... to kGkqpvcPI1TGmR4Sc... (flutter/engine#46079)
2023-09-20 godofredoc@google.com Use magic envs to pass commit and temp folder. (flutter/engine#46015)

Also rolling transitive DEPS:
  fuchsia/sdk/core/mac-amd64 from 06g6i7-5u8O- to kGkqpvcPI1TG

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 jonahwilliams@google.com,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://bugs.chromium.org/p/skia/issues/entry?template=Autoroller+Bug

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

bin/internal/engine.version

-5a924a9017d764bc5c08d21a76f6ab52bba3a6f1
+81b93fc4a2cc02f067acfe19574eb2ccc316fed7

bin/internal/fuchsia-mac.version

-06g6i7-5u8O-FOTSiXV49zPhENc4ZaXzGkSyFuDpJQgC
+kGkqpvcPI1TGmR4Scp19EXK5hxyrDBhn2-hp4U8E6skC