Fix #261 SocketModeHandler#start() does not terminate on Windows

[seratch]

This pull request resolves #261 by adding an extra logic for Windows OS. Refer to https://bugs.python.org/issue35935 for details.

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

• slack_bolt.App and/or its core components
• slack_bolt.async_app.AsyncApp and/or its core components
• Adapters in slack_bolt.adapter
• Document pages under /docs
• Others

Requirements (place an x in each [ ])

Please read the Contributing guidelines and Code of Conduct before creating this issue or pull request. By submitting, you are agreeing to those rules.

• 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 ./scripts/install_all_and_run_tests.sh after making the changes.

[codecov]

Codecov Report

Merging #262 (418506e) into main (dafc833) will decrease coverage by 0.03%.
The diff coverage is 50.00%.

❗ Current head 418506e differs from pull request most recent head a59d1e0. Consider uploading reports for the commit a59d1e0 to get more accurate results

@@            Coverage Diff             @@
##             main     #262      +/-   ##
==========================================
- Coverage   91.28%   91.25%   -0.04%     
==========================================
  Files         160      160              
  Lines        4979     4983       +4     
==========================================
+ Hits         4545     4547       +2     
- Misses        434      436       +2     

Impacted Files	Coverage Δ
slack_bolt/adapter/socket_mode/base_handler.py	62.96% <50.00%> (-2.26%)	⬇️

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