[MINOR][DOCS] Fix ForEachWriter Java example

### What changes were proposed in this pull request?
Structured streaming documentation example fix

### Why are the changes needed?
Currently the java example uses incorrect syntax

### Does this PR introduce any user-facing change?
Yes

### How was this patch tested?
In IDE

Closes #27671 from roland1982/foreachwriter_java_example_fix.

Authored-by: roland-ondeviceresearch <roland@ondeviceresearch.com>
Signed-off-by: HyukjinKwon <gurwls223@apache.org>

docs/structured-streaming-programming-guide.md

@@ -2156,7 +2156,7 @@ streamingDatasetOfString.writeStream.foreach(
 In Java, you have to extend the class `ForeachWriter` ([docs](api/java/org/apache/spark/sql/ForeachWriter.html)).
 {% highlight java %}
 streamingDatasetOfString.writeStream().foreach(
-  new ForeachWriter[String] {
+  new ForeachWriter<String>() {
 
     @Override public boolean open(long partitionId, long version) {
       // Open connection