Increase docs number in disk usage for vectors (#95470)

Closes #95045

Author: mayya-sharipova

server/src/test/java/org/elasticsearch/action/admin/indices/diskusage/IndexDiskUsageAnalyzerTests.java

@@ -252,7 +252,7 @@ public void testKnnVectors() throws Exception {
         try (Directory dir = createNewDirectory()) {
             final CodecMode codec = randomFrom(CodecMode.values());
             VectorSimilarityFunction similarity = randomFrom(VectorSimilarityFunction.values());
-            int numDocs = between(100, 1000);
+            int numDocs = between(1000, 5000);
             int dimension = between(10, 200);
 
             indexRandomly(dir, codec, numDocs, doc -> {