Fix #1025 websocket_client based SocketModeClient may fail in on_close callback

[seratch]

Summary

This pull request fixes #1025 by updating the internal method signature of on_close listeners. It seems that this callback may not be called in common patterns (we don't have any unit tests reproducing the error). But when it's called, the current implementation is not compatible.

References:

• https://github.com/websocket-client/websocket-client/blob/v1.0.1/websocket/tests/test_app.py#L158-L159
• https://github.com/websocket-client/websocket-client/blob/v1.0.1/docs/source/examples.rst

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.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)
• /docs-src (Documents, have you run ./docs.sh?)
• /docs-src-v2 (Documents, have you run ./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 python setup.py validate after making the changes.

[codecov]

Codecov Report

Merging #1026 (2bff457) into main (97a5250) will not change coverage.
The diff coverage is 0.00%.

@@           Coverage Diff           @@
##             main    #1026   +/-   ##
=======================================
  Coverage   83.66%   83.66%           
=======================================
  Files          95       95           
  Lines        8792     8792           
=======================================
  Hits         7356     7356           
  Misses       1436     1436           

Impacted Files	Coverage Δ
slack_sdk/socket_mode/websocket_client/__init__.py	60.76% <0.00%> (ø)

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