[java] Fix avro bytes conversion for BQ storage (#33412)

Avro byte is represented with java ByteBuffer.
Current implementation expects a byte array. This fails in practice with
a ClassCastException: class java.nio.HeapByteBuffer cannot be cast to class [B

sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/bigquery/AvroGenericRecordToStorageApiProto.java

@@ -86,7 +86,7 @@ public class AvroGenericRecordToStorageApiProto {
           .put(Schema.Type.STRING, Object::toString)
           .put(Schema.Type.BOOLEAN, Function.identity())
           .put(Schema.Type.ENUM, o -> o.toString())
-          .put(Schema.Type.BYTES, o -> ByteString.copyFrom((byte[]) o))
+          .put(Schema.Type.BYTES, o -> ByteString.copyFrom(((ByteBuffer) o).duplicate()))
           .build();
 
   // A map of supported logical types to their encoding functions.

sdks/java/io/google-cloud-platform/src/test/java/org/apache/beam/sdk/io/gcp/bigquery/AvroGenericRecordToStorageApiProtoTest.java

@@ -28,6 +28,7 @@
 import com.google.protobuf.Descriptors;
 import com.google.protobuf.DynamicMessage;
 import java.math.BigDecimal;
+import java.nio.ByteBuffer;
 import java.nio.charset.StandardCharsets;
 import java.security.MessageDigest;
 import java.security.NoSuchAlgorithmException;
@@ -308,7 +309,7 @@ enum TestEnum {
       Instant now = Instant.now();
       baseRecord =
           new GenericRecordBuilder(BASE_SCHEMA)
-              .set("bytesValue", BYTES)
+              .set("bytesValue", ByteBuffer.wrap(BYTES))
               .set("intValue", (int) 3)
               .set("longValue", (long) 4)
               .set("floatValue", (float) 3.14)