Invoke Flyway#setCallbacks only if necessary

Closes gh-14775

Author: snicoll

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/flyway/FlywayAutoConfiguration.java

@@ -149,7 +149,9 @@ else if (this.flywayDataSource != null) {
 			else {
 				flyway.setDataSource(this.dataSource);
 			}
-			flyway.setCallbacks(this.flywayCallbacks.toArray(new FlywayCallback[0]));
+			if (!this.flywayCallbacks.isEmpty()) {
+				flyway.setCallbacks(this.flywayCallbacks.toArray(new FlywayCallback[0]));
+			}
 			String[] locations = new LocationResolver(flyway.getDataSource())
 					.resolveLocations(this.properties.getLocations());
 			checkLocationExists(locations);