Fix #1099 by locking pytype version

[seratch]

This pull request resolves #1099 -- pytype outputs can be different in newer versions, therefore we should lock its version for stable execution.

Thanks @srtaalej for reporting it!

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
• [x] 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.

• [x] I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• [x] I've read and agree to the Code of Conduct.
• [x] I've run ./scripts/install_all_and_run_tests.sh after making the changes.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 91.77%. Comparing base (b88d0fc) to head (0139d45).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1100 +/- ## ======================================= Coverage 91.77% 91.77% ======================================= Files 186 186 Lines 6407 6407 ======================================= Hits 5880 5880 Misses 527 527 ```

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