Creating a subtask does not create a 'X created blocking task Y' message in the parent task.

For example:

• https://phabricator.wikimedia.org/T90574 was created using the 'Create Subtask' button on https://phabricator.wikimedia.org/T90534 .
  • No message 'valhallasw created a blocking task: T90574' is shown
• https://phabricator.wikimedia.org/T90535 was linked explicitly using 'add a blocking task'
  • The message 'yuvipanda added a blocked task: T90535' is shown

Steps to reproduce:

• On task A, click 'Create subtask'
• Create a new task
• Go back to task A
• There is no news message

Expected behavior:

• Some message is shown on the parent task