Update StandardMessageCodec.readValue to be @Nullable (#53473)

corrects StandardMessageCodec return nullability annotation.

shell/platform/android/io/flutter/plugin/common/StandardMessageCodec.java

diff --git a/shell/platform/android/io/flutter/plugin/common/StandardMessageCodec.java b/shell/platform/android/io/flutter/plugin/common/StandardMessageCodec.java
index 7e1978e..c13b568 100644
--- a/shell/platform/android/io/flutter/plugin/common/StandardMessageCodec.java
+++ b/shell/platform/android/io/flutter/plugin/common/StandardMessageCodec.java
@@ -331,7 +331,7 @@
   }
 
   /** Reads a value as written by writeValue. */
-  @NonNull
+  @Nullable
   protected final Object readValue(@NonNull ByteBuffer buffer) {
     if (!buffer.hasRemaining()) {
       throw new IllegalArgumentException("Message corrupted");