Unpin moto, and support moto 5.0 changes

[s-t-e-v-e-n-k]

To stop testing with old versions of moto, unpin it from version 3, to the latest, and also change the test cases to cope with the new changes.

Category (place an x in each of the [ ])

• slack_sdk.web.WebClient (sync/async) (Web API client)
• slack_sdk.webhook.WebhookClient (sync/async) (Incoming Webhook, response_url sender)
• slack_sdk.socket_mode (Socket Mode client)
• slack_sdk.signature (Request Signature Verifier)
• slack_sdk.oauth (OAuth Flow Utilities)
• slack_sdk.models (UI component builders)
• slack_sdk.scim (SCIM API client)
• slack_sdk.audit_logs (Audit Logs API client)
• slack_sdk.rtm_v2 (RTM client)
• /docs-src (Documents, have you run ./scripts/docs.sh?)
• /docs-src-v2 (Documents, have you run ./scripts/docs-v2.sh?)
• /tutorial (PythOnBoardingBot tutorial)
• tests/integration_tests (Automated tests for this library)

Requirements (place an x in each [ ])

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.
• I've run python3 -m venv .venv && source .venv/bin/activate && ./scripts/run_validation.sh after making the changes.

[salesforce-cla]

Thanks for the contribution! Before we can merge this, we need @s-t-e-v-e-n-k to sign the Salesforce Inc. Contributor License Agreement.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (60b02d6) 85.33% compared to head (b0e4026) 85.41%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1463      +/-   ##
==========================================
+ Coverage   85.33%   85.41%   +0.08%     
==========================================
  Files         111      111              
  Lines       12289    12289              
==========================================
+ Hits        10487    10497      +10     
+ Misses       1802     1792      -10     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[WilliamBergamin]

Hi @s-t-e-v-e-n-k thank you for the contribution 💯 unfortunately these change would require that we drop support for python 3.6 and 3.7 which would require a major version bump and a deprecation notice
As of our latest data analysis it seem like there are still 10-15% of our developers that use python 3.6 and 3.7, since this tool is used internally by customers we try to be as generous as possible with regard to version support

If you can make these changes compatible with python 3.6 and 3.7 I will be able to approve them

[s-t-e-v-e-n-k]

@WilliamBergamin Thanks for the quick review! I've adapted my changes to support 3.6 and 3.7.

[WilliamBergamin]

This is awesome, thank you 💯 requesting one change more change but then we should be good to ship

[WilliamBergamin]

LGTM 💯