[AIRFLOW-1840] and [AIRFLOW-2495] increment celery to >4.1.0 (current release is 4.1.1)

[cloneluke]

…tay under 4.2.0 until that and/or 5.0 is tested.

[AIRFLOW-1840]
#2806
also related to #3388
[AIRFLOW-2495]

Make sure you have checked all steps below.

JIRA

• [ X] My PR addresses the following Airflow JIRA issues and references them in the PR title. For example, "[AIRFLOW-XXX] My Airflow PR"
  • https://issues.apache.org/jira/browse/AIRFLOW-XXX
  • In case you are fixing a typo in the documentation you can prepend your commit with [AIRFLOW-XXX], code changes always need a JIRA issue.

Description

• Here are some details about my PR, including screenshots of any UI changes:
  incrementing celery to >4.1.0 (current release is 4.1.1) but making it stay under 4.2.0 until that and/or 5.0 is tested.

Tests

• My PR adds the following unit tests OR does not need testing for this extremely good reason:

Commits

• [X ] My commits all reference JIRA issues in their subject lines, and I have squashed multiple commits if they address the same issue. In addition, my commits follow the guidelines from "How to write a good git commit message":
  1. Subject is separated from body by a blank line
  2. Subject is limited to 50 characters
  3. Subject does not end with a period
  4. Subject uses the imperative mood ("add", not "adding")
  5. Body wraps at 72 characters
  6. Body explains "what" and "why", not "how"

Documentation

• In case of new functionality, my PR adds documentation that describes how to use it.
  • When adding new operators/hooks/sensors, the autoclass documentation generation needs to be added.

Code Quality

• Passes git diff upstream/master -u -- "*.py" | flake8 --diff

[Fokko]

Thanks @cloneluke

Could you pay attention to the commit message guidelines in the commit template?

[cloneluke]

duplicate to #3439 please close