Fix #177 by updating App/AsyncApp bot_only flag initialization

[seratch]

This pull request fixes #177 - see the issue 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-io]

Codecov Report

Merging #178 (e23f340) into main (890cf3f) will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #178      +/-   ##
==========================================
+ Coverage   91.72%   91.76%   +0.04%     
==========================================
  Files         149      149              
  Lines        4434     4446      +12     
==========================================
+ Hits         4067     4080      +13     
+ Misses        367      366       -1     

Impacted Files	Coverage Δ
slack_bolt/app/app.py	86.89% <100.00%> (+0.17%)	⬆️
slack_bolt/app/async_app.py	94.83% <100.00%> (+0.07%)	⬆️
slack_bolt/logger/messages.py	88.37% <100.00%> (+0.56%)	⬆️
...e/authorization/async_multi_teams_authorization.py	91.17% <0.00%> (+2.94%)	⬆️

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