chore: roll Dart to 3.6.1

Author: felangel

DEPS

@@ -15,7 +15,7 @@ vars = {
   'skia_git': 'https://skia.googlesource.com',
   'llvm_git': 'https://llvm.googlesource.com',
   'skia_revision': '6062afaa505bf7e6c727a20cafe4c7bee0f02df8',
-  "dart_sdk_revision": "4f9b5084a041a0e7cc26295da1da9109df43ac4c",
+  "dart_sdk_revision": "5c6f8122c1ee85f833ea3b69b3b85dc07303e8d2",
   "dart_sdk_git": "git@github.com:shorebirdtech/dart-sdk.git",
   "updater_git": "https://github.com/shorebirdtech/updater.git",
   "updater_rev": "71b5ed65fab03fcf241edf0c74d027de9998da51",