fix: Rename send_activation_email task (step 3/3) (#26329)
fix: Rename send_activation_email task (step 3/3) (#26329)

The old name was
`student.send_activation_email`.

The new name is now
`common.djangoapps.student.tasks.send_activation_email`.

We no longer user the old task name,
so we can safely stop registering it with Celery
workers, without fear of dropping any lingering
tasks under the old name.
edx/edx-platform,angelapper/edx-platform,stvstnfrd/edx-platform,eduNEXT/edx-platform,stvstnfrd/edx-platform,eduNEXT/edunext-platform,eduNEXT/edunext-platform,arbrandes/edx-platform,edx/edx-platform,eduNEXT/edx-platform,angelapper/edx-platform,stvstnfrd/edx-platform,edx/edx-platform,arbrandes/edx-platform,EDUlib/edx-platform,eduNEXT/edx-platform,EDUlib/edx-platform,angelapper/edx-platform,arbrandes/edx-platform,edx/edx-platform,stvstnfrd/edx-platform,eduNEXT/edunext-platform,eduNEXT/edunext-platform,EDUlib/edx-platform,EDUlib/edx-platform,arbrandes/edx-platform,eduNEXT/edx-platform,angelapper/edx-platform