Roll Fuchsia SDK from 27.20250221.4.1 to 27.20250221.6.1

If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/fuchsia-sdk-dart-sdk
Please CC fuchsia-3p-engprod@google.com on the revert to ensure that a human
is aware of the problem.

To file a bug in Fuchsia SDK: https://bugs.fuchsia.dev/p/fuchsia/issues/list
To file a bug in Dart SDK: https://github.com/dart-lang/sdk/issues

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

Cq-Include-Trybots: luci.dart.try:vm-fuchsia-release-x64-try;luci.dart.try:vm-fuchsia-release-arm64-try
Change-Id: Ia39f02036d576fb5d8ffc7b92e27634faf264f92
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/411123
Reviewed-by: Siva Annamalai <asiva@google.com>
Commit-Queue: Alexander Aprelev <aam@google.com>
Reviewed-by: Zijie He <zijiehe@google.com>
Reviewed-by: Alexander Aprelev <aam@google.com>

DEPS

@@ -85,7 +85,7 @@ vars = {
   "download_reclient": True,
 
   # Update from https://chrome-infra-packages.appspot.com/p/fuchsia/sdk/core
-  "fuchsia_sdk_version": "version:27.20250221.4.1",
+  "fuchsia_sdk_version": "version:27.20250221.6.1",
   "download_fuchsia_deps": False,
 
   # Ninja, runs the build based on files generated by GN.