Fix the cancel tasks

[bernardusrendy]

Summary

Include a summary of major changes in bullet points:

• Feature 1
• Feature 2
• Fix 1
• Fix 2

Additional dependencies introduced (if any)

• List all new dependencies needed and justify why. While adding dependencies that bring
  significantly useful functionality is perfectly fine, adding ones that add trivial
  functionality, e.g., to use one single easily implementable function, is frowned upon.
  Provide a justification why that dependency is needed. Especially frowned upon are
  circular dependencies.

TODO (if any)

If this is a work-in-progress, write something about what else needs to be done.

• Feature 1 supports A, but not B.

Checklist

Work-in-progress pull requests are encouraged, but please put [WIP] in the pull request
title.

Before a pull request can be merged, the following items must be checked:

• Code is in the standard Python style.
  The easiest way to handle this is to run the following in the correct sequence on
  your local machine. Start with running black on your new code. This will
  automatically reformat your code to PEP8 conventions and removes most issues. Then run
  pycodestyle, followed by flake8.
• Docstrings have been added in theNumpy docstring format.
  Run pydocstyle on your code.
• Type annotations are highly encouraged. Run mypy to
  type check your code.
• Tests have been added for any new functionality or bug fixes.
• All linting and tests pass.

Note that the CI system will run all the above checks. But it will be much more
efficient if you already fix most errors prior to submitting the PR. It is highly
recommended that you use the pre-commit hook provided in the repository. Simply
cp pre-commit .git/hooks and a check will be run prior to allowing commits.