Unblock PowerShell Script before execution (#17658)

bin/flutter.bat

diff --git a/bin/flutter.bat b/bin/flutter.bat
index ed81a65..0c8c7c0 100644
--- a/bin/flutter.bat
+++ b/bin/flutter.bat
@@ -91,7 +91,7 @@
     SET update_dart_bin=%FLUTTER_ROOT%/bin/internal/update_dart_sdk.ps1
     REM Escape apostrophes from the executable path
     SET "update_dart_bin=!update_dart_bin:'=''!"
-    CALL PowerShell.exe -ExecutionPolicy Bypass -Command "& '%update_dart_bin%'"
+    CALL PowerShell.exe -ExecutionPolicy Bypass -Command "Unblock-File -Path '%update_dart_bin%'; & '%update_dart_bin%'"
     IF "%ERRORLEVEL%" NEQ "0" (
       ECHO Error: Unable to update Dart SDK. Retrying...
       timeout /t 5 /nobreak