This will ensure that errors raised by these tasks will alert the right
team. `send_course_enrollment_email` is the one I set out to fix, but I
discovered a few others.
I located tasks that were missing decorators by running the following
search and visually inspecting the results, although semgrep might be able
to do better:
```
ack '^@.*task|^@set_code_owner_attribute' cms lms common openedx xmodule --ignore-dir=tests --python
```
Also, add more detailed explanation of why a couple of tasks can't use the
decorator. This should only be an issue on tasks inheriting from
UserTaskMixin, which in practice is just CourseExportTask and
CourseImportTask (and the apparently unused EnrollmentReadTask and
EnrollmentWriteTask), via UserTask.
It's long past time that the default test modulestore was Split,
instead of Old Mongo. This commit switches the default store and
fixes some tests that now fail:
- Tests that didn't expect MFE to be enabled (because we don't
enable MFE for Old Mongo) - opt out of MFE for those
- Tests that hardcoded old key string formats
- Lots of other random little differences
In many places, I didn't spend much time trying to figure out how to
properly fix the test, and instead just set the modulestore to Old
Mongo.
For those tests that I didn't spend time investigating, I've set
the modulestore to TEST_DATA_MONGO_AMNESTY_MODULESTORE - search for
that string to find further work.
