[Docs] Update method setSource(byte[] source) (#26561)

The method setSource(byte[]) from the type IndexRequestBuilder is deprecated,
use the method setSource(byte[] source, XContentType xContentType).

docs/java-api/docs/index_.asciidoc

@@ -140,7 +140,7 @@ String json = "{" +
     "}";
 
 IndexResponse response = client.prepareIndex("twitter", "tweet")
-        .setSource(json)
+        .setSource(json, XContentType.JSON)
         .get();
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