Add cast to prepare for package:file update (#33268)

packages/flutter_tools/lib/src/devfs.dart

diff --git a/packages/flutter_tools/lib/src/devfs.dart b/packages/flutter_tools/lib/src/devfs.dart
index b040dc8..bcc6e59 100644
--- a/packages/flutter_tools/lib/src/devfs.dart
+++ b/packages/flutter_tools/lib/src/devfs.dart
@@ -46,7 +46,7 @@
   Stream<List<int>> contentsAsStream();
 
   Stream<List<int>> contentsAsCompressedStream() {
-    return contentsAsStream().transform<List<int>>(gzip.encoder);
+    return contentsAsStream().cast<List<int>>().transform<List<int>>(gzip.encoder);
   }
 
   /// Return the list of files this content depends on.