Fix testFollowerBehaviour (elastic#96257)

The test was failing when responseDelay == leaderCheckTimeoutMillis.
This resulted in scheduling both handling the response and timeout at the same
mills and executing them in random order. The fix makes it impossible to
reply the same time as request is timeout as the behavior is not deterministic
 in such case.

Author: idegtiarenko

server/src/test/java/org/elasticsearch/cluster/coordination/LeaderCheckerTests.java

@@ -115,10 +115,14 @@ protected void onSendRequest(long requestId, String action, TransportRequest req
                 super.onSendRequest(requestId, action, request, node);
 
                 final boolean mustSucceed = leaderCheckRetryCount - 1 <= consecutiveFailedRequestsCount;
-                final long responseDelay = randomLongBetween(0, leaderCheckTimeoutMillis + (mustSucceed ? -1 : 60000));
+                final long responseDelay = randomValueOtherThan(
+                    leaderCheckTimeoutMillis,
+                    () -> randomLongBetween(0, leaderCheckTimeoutMillis + (mustSucceed ? -1 : 60000))
+                );
                 final boolean successResponse = allResponsesFail.get() == false && (mustSucceed || randomBoolean());
 
-                if (responseDelay >= leaderCheckTimeoutMillis) {
+                assert responseDelay != leaderCheckTimeoutMillis;
+                if (responseDelay > leaderCheckTimeoutMillis) {
                     timeoutCount.incrementAndGet();
                     consecutiveFailedRequestsCount += 1;
                 } else if (successResponse == false) {