test(webpush): Add integration test for webpush that shows the mozart…

[nickvergessen]

… 1.2.1 bug

• Ref build(deps): Bump coenjacobs/mozart from 1.0.6 to 1.2.1 in /vendor-bin/mozart #2881 (review)
• Ref fix: Fix issue with alias qualified names coenjacobs/mozart#380

[nickvergessen]

Tested locally with 1.2.1 and it shows the error:

[Tue Mar 31 13:39:32 2026] 127.0.0.1:60132 [500]: POST /ocs/v2.php/apps/notifications/api/v2/webpush?format=json
[Tue Mar 31 13:39:32 2026] 127.0.0.1:60132 Closing
    Given user "test1" registers for webpush with                  # FeatureContext::registerForWebPush()
      | endpoint    | https://push.example.com/test |
      | uaPublicKey | VALID_KEY                     |
      | auth        | VALID_AUTH                    |
      | appTypes    | all                           |
      Server error: `POST http://localhost:8080/ocs/v2.php/apps/notifications/api/v2/webpush?format=json` resulted in a `500 Internal Server Error` response:
      {"ocs":{"meta":{"status":"failure","statuscode":996,"message":"Internal Server Error\nClass \"OCA\\Notifications\\Vendor (truncated...)
       (GuzzleHttp\Exception\ServerException)