missing return type declaration for getSubscribedEvents()

Problem/Motivation

while writing automated tests, I came across the following error message:

Method "Symfony\Component\EventDispatcher\EventSubscriberInterface::getSubscribedEvents()" might add "array" as a native return type declaration in the future. Do the same in implementation "Drupal\views_bulk_operations\EventSubscriber\ViewsBulkOperationsEventSubscriber" now to avoid errors or add an explicit @return annotation to suppress this message.

Steps to reproduce

1. write a module that includes a view
2. add VBO to your module's view
3. write automated tests
4. run your tests with the --verbose flag

Proposed resolution

I'll be forking a simple patch shortly to fix the required function calls adding the array return type as expected by PHPUnit to future-proof the getSubscribedEvents() implementation.

Remaining tasks

1. create an issue fork (me)
2. test the patch as follows:
   1. apply the patch
   2. create a simple module with a VBO-powered view in config/install
   3. write a test for your view
   4. run your test with the --verbose flag