Eliminate the Task.all_tasks() warning in the CI Tests

[Imod7]

Python version:
Python 3.6
Python 3.7
Python 3.8

Operating system (windows, osx, ...):
Ubuntu
Windows

Issue:
This Issue is part of the effort to close the Issue#7738 hence to reduce the amount of warnings that are raised when running all tests in the CI. From a first investigation, it seems that this warning (PendingDeprecationWarning: Task.all_tasks() is deprecated, use asyncio.all_tasks() instead...) for which the current Issue was opened, had 46 occurrences but in a latest CI run it appears in only ~27 tests.

Error (including full traceback):

2021-03-15T14:21:47.6645370Z tests/test_train.py: 27 warnings
2021-03-15T14:21:47.6646399Z   /home/runner/work/rasa/rasa/rasa/utils/common.py:310: PendingDeprecationWarning: Task.all_tasks() is deprecated, use asyncio.all_tasks() instead
2021-03-15T14:21:47.6647500Z     pending = asyncio.Task.all_tasks()

Possible Solutions:

• As indicated in the Deprecation message, first step it would be to replace the Task.all_tasks() call with asyncio.all_tasks().
• This however introduces another error

E           RuntimeError: no running event loop

which would need to be addressed.

• Related docs

Command or request that led to error:

• The warning can be found in any of the following CI tests log files :
  • 32_Run Tests (test-full-model-training, ubuntu-latest, 3.7).txt
  • 33_Run Tests (test-full-model-training, ubuntu-latest, 3.8).txt
  • 35_Run Tests (test-full-model-training, windows-latest, 3.7).txt
• Also, the warning can be reproduced when running one of the tests below:

pytest tests/test_train.py::TestE2e::test_e2e_gives_experimental_warning
pytest tests/test_telemetry.py::test_events_schema

Definition of Done:

• The PendingDeprecationWarning: Task.all_tasks() does not appear anymore.