Update mypy to 0.920

[carmocca]

What does this PR do?

Fixes failures after the mypy 0.920 release

Does your PR introduce any breaking changes? If yes, please list them.

None

Before submitting

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• [n/a] Did you make sure to update the documentation with your changes? (if necessary)
• [n/a] Did you write any new necessary tests? (not for typos and docs)
• Did you verify new and existing tests pass locally with your changes?
• Did you list all the breaking changes introduced by this pull request?
• [n/a] Did you update the CHANGELOG? (not for typos, docs, test updates, or internal minor changes/refactorings)

PR review

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cc @carmocca @akihironitta @Borda

[github-actions]

Build Error! No Linked Issue found. Please link an issue or mention it in the body using #<issue_id>