Avoid string conversion in ExecutionContextSerializer tests

Avoid the byte to string to byte conversion in
AbstractExecutionContextSerializerTests.

spring-batch-core/src/test/java/org/springframework/batch/core/repository/dao/AbstractExecutionContextSerializerTests.java

@@ -166,9 +166,7 @@ protected Map<String, Object> serializationRoundTrip(Map<String, Object> m1) thr
         ByteArrayOutputStream out = new ByteArrayOutputStream();
         getSerializer().serialize(m1, out);
 
-        String s = new String(out.toByteArray(), "ISO-8859-1");
-
-        InputStream in = new ByteArrayInputStream(s.getBytes("ISO-8859-1"));
+        InputStream in = new ByteArrayInputStream(out.toByteArray());
         Map<String, Object> m2 = getSerializer().deserialize(in);
         return m2;
     }