[Doctrine][DependencyInjection] Make a test less fragile.

The test checks that a few items are ordered according to the value of their 'priority' attribute. However, a few of the items have the same value of this attribute. RegisterEventListenersAndSubscribersPass doesn't use a stable sorting, yet the test asserts that items that are 'equal' shall go in the original order. Modified so that the order of the original items is not checked.

| Q             | A
| ------------- | ---
| Bug fix?      | [no]
| New feature?  | [no]
| BC breaks?    | [no]
| Deprecations? | [no]
| Tests pass?   | [yes]
| Fixed tickets | [none]
| License       | MIT
| Doc PR        | [none]