Update iOS project migration help URL (#51973)

packages/flutter_tools/lib/src/ios/mac.dart

@@ -458,7 +458,7 @@ Future<void> diagnoseXcodeBuildFailure(XcodeBuildResult result) async {
       && result.stdout?.contains('but the linked and embedded framework') == true
       && result.stdout?.contains('was built for iOS') == true) {
     globals.printError('');
-    globals.printError('Your Xcode project requires migration. See https://github.com/flutter/flutter/issues/50568 for details.');
+    globals.printError('Your Xcode project requires migration. See https://flutter.dev/docs/development/ios-project-migration for details.');
     globals.printError('');
     globals.printError('You can temporarily work around this issue by running:');
     globals.printError('  rm -rf ios/Flutter/App.framework');

packages/flutter_tools/lib/src/ios/migrations/remove_framework_link_and_embedding_migration.dart

@@ -102,7 +102,7 @@ class RemoveFrameworkLinkAndEmbeddingMigration extends IOSMigrator {
       // Print scary message if the user is on Xcode 11.4 or greater, or if Xcode isn't installed.
       final bool xcodeIsInstalled = _xcode.isInstalled;
       if(!xcodeIsInstalled || (_xcode.majorVersion > 11 || (_xcode.majorVersion == 11 && _xcode.minorVersion >= 4))) {
-        logger.printError('Your Xcode project requires migration. See https://github.com/flutter/flutter/issues/50568 for details.');
+        logger.printError('Your Xcode project requires migration. See https://flutter.dev/docs/development/ios-project-migration for details.');
         return false;
       }
     }