Disable deprecated flake8-mypy Python tox check

[jdeamicis]

Description of changes

• Disable deprecated flake8-mypy Python tox check, which caused problems in the GitHub actions on the repository.

References

• Disable deprecated flake8-mypy Python tox check aws-parallelcluster#5750
• Disable deprecated flake8-mypy Python tox check aws-parallelcluster-node#571

Checklist

• Make sure you are pointing to the right branch.
• If you're creating a patch for a branch other than develop add the branch name as prefix in the PR title (e.g. [release-3.6]).
• Check all commits' messages are clear, describing what and why vs how.
• Make sure to have added unit tests or integration tests to cover the new/modified code.
• Check if documentation is impacted by this change.

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