version 3.20.1

Changes

• #1343 Fix #1342 files_upload_v2 fails to share files in a channel - Thanks @peanutbutter97 @mshinji @plenti-chris-fowles @fukumoto-ts @seratch

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• All issues/pull requests: https://github.com/slackapi/python-slack-sdk/milestone/77?closed=1
• All changes: v3.20.0...v3.20.1