Upgrade pytype version to the latest

[seratch]

This pull request upgrades "pytype" code validator to 2022.4.15 plus updates the code to be compatible with the version.

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 #636 (e5676f4) into main (02c3520) will not change coverage.
The diff coverage is 0.00%.

@@           Coverage Diff           @@
##             main     #636   +/-   ##
=======================================
  Coverage   92.09%   92.09%           
=======================================
  Files         170      170           
  Lines        5791     5791           
=======================================
  Hits         5333     5333           
  Misses        458      458           

Impacted Files	Coverage Δ
slack_bolt/app/app.py	87.72% <0.00%> (ø)

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