HSEARCH-4687 Raise the timeout for background indexing completion in …

…tests to 30s

Because some tests are quite slow on some databases (e.g. CockroachDB)

util/internal/integrationtest/common/src/main/java/org/hibernate/search/util/impl/integrationtest/common/rule/BackendIndexingWorkExpectations.java

@@ -78,7 +78,7 @@ public void awaitBackgroundIndexingCompletion(CompletableFuture<?> completion) {
 					// We're only waiting for in-memory state to change,
 					// so it's fine to poll aggressively every 5ms.
 					.pollInterval( Duration.ofMillis( 5 ) )
-					.atMost( Duration.ofSeconds( 15 ) )
+					.atMost( Duration.ofSeconds( 30 ) )
 					.until( completion::isDone );
 		}
 	}