Fix random failure in SearchRequestTests#testRandomVersionSerialization (elastic#42069)

This commit fixes a test bug that ends up comparing the result of two consecutive calls to System.currentTimeMillis that can be different
on slow CIs.

Closes elastic#42064

Author: jimczi

server/src/main/java/org/elasticsearch/action/search/SearchRequest.java

@@ -302,12 +302,19 @@ boolean isFinalReduce() {
      * ensure that the same value, determined by the coordinating node, is used on all nodes involved in the execution of the search
      * request. When created through {@link #crossClusterSearch(SearchRequest, String[], String, long, boolean)}, this method returns
      * the provided current time, otherwise it will return {@link System#currentTimeMillis()}.
-     *
      */
     long getOrCreateAbsoluteStartMillis() {
         return absoluteStartMillis == DEFAULT_ABSOLUTE_START_MILLIS ? System.currentTimeMillis() : absoluteStartMillis;
     }
 
+    /**
+     * Returns the provided <code>absoluteStartMillis</code> when created through {@link #crossClusterSearch} and
+     * -1 otherwise.
+     */
+    long getAbsoluteStartMillis() {
+        return absoluteStartMillis;
+    }
+
     /**
      * Sets the indices the search will be executed on.
      */

server/src/test/java/org/elasticsearch/action/search/SearchRequestTests.java

@@ -94,7 +94,7 @@ public void testRandomVersionSerialization() throws IOException {
             assertTrue(deserializedRequest.isFinalReduce());
         } else {
             assertEquals(searchRequest.getLocalClusterAlias(), deserializedRequest.getLocalClusterAlias());
-            assertEquals(searchRequest.getOrCreateAbsoluteStartMillis(), deserializedRequest.getOrCreateAbsoluteStartMillis());
+            assertEquals(searchRequest.getAbsoluteStartMillis(), deserializedRequest.getAbsoluteStartMillis());
             assertEquals(searchRequest.isFinalReduce(), deserializedRequest.isFinalReduce());
         }
     }