Drop Support for EOL Python 3.6, 3.7 and 3.8

As of today per Python Software Foundation policy here: https://devguide.python.org/versions/

• Python 3.6 has ended security support and it's end of life was - 2021-12-23. It's 3 years unsupported!
• Python 3.7 has ended security support and it's end of life was - 2023-06-27. It's 1.5 years unsupported!
• Python 3.8 has ended security support and it's end of life was - 2024-10-07. It's 3 months unsupported!

Does Slack SDK plans to remove support for those Python versions? Promoting unsupported version of Python has security concerns and it shouldn't be promoted.

I've realised this while working on #1633 as I wasn't expecting that Python 3.6 is in use and I was using features that were added in Python 3.8 so I lived under assumption that I can use everything from 3.9 and above.

Category

• slack_sdk.web.WebClient (sync/async) (Web API client)
• slack_sdk.webhook.WebhookClient (sync/async) (Incoming Webhook, response_url sender)
• slack_sdk.models (UI component builders)
• slack_sdk.oauth (OAuth Flow Utilities)
• slack_sdk.socket_mode (Socket Mode client)
• slack_sdk.audit_logs (Audit Logs API client)
• slack_sdk.scim (SCIM API client)
• slack_sdk.rtm (RTM client)
• slack_sdk.signature (Request Signature Verifier)

Requirements

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Non sono indicati file, test o punti di ingresso. Inizia esaminando la configurazione del progetto e i riferimenti CI alle versioni di Python supportate, quindi analizza i componenti SDK elencati per verificarne il supporto specifico per versione. Il lavoro è completato quando Python 3.6, 3.7 e 3.8 non sono più supportati in modo coerente in questi componenti e la relativa validazione è aggiornata.