(Describe the goal of this PR. Mention any related Issue numbers)

### 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](https://github.com/slackapi/bolt-python/blob/main/.github/contributing.md) and [Code of Conduct](https://slackhq.github.io/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](https://github.com/slackapi/bolt-python/blob/main/.github/contributing.md) and have done my best effort to follow them.
* [ ] I've read and agree to the [Code of Conduct](https://slackhq.github.io/code-of-conduct).
* [ ] I've run `./scripts/install_all_and_run_tests.sh` after making the changes.
