Run mypy with falcon 4.x

[seratch]

This pull request closes #1197

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

Attention: Patch coverage is 50.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 90.93%. Comparing base (f6fc477) to head (b354ae3).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
slack_bolt/adapter/falcon/resource.py	33.33%	2 Missing ⚠️
slack_bolt/adapter/falcon/async_resource.py	66.66%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1199   +/-   ##
=======================================
  Coverage   90.93%   90.93%           
=======================================
  Files         222      222           
  Lines        7505     7505           
=======================================
  Hits         6825     6825           
  Misses        680      680           

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