Fix an issue where different user's token may exist in context

[seratch]

This pull request resolves a bug where different user's user token (xoxp- prefixed token) may exist in context.user_token while context.user_id is consistent with an incoming request. This issue affects only when an app uses an InstallationStore. As this issue can be critical in some situations, I will release a patch version shortly.

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 #244 (8cff029) into main (a69abb5) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #244   +/-   ##
=======================================
  Coverage   91.36%   91.36%           
=======================================
  Files         160      160           
  Lines        4967     4971    +4     
=======================================
+ Hits         4538     4542    +4     
  Misses        429      429           

Impacted Files	Coverage Δ
slack_bolt/authorization/async_authorize.py	86.95% <100.00%> (+0.28%)	⬆️
slack_bolt/authorization/authorize.py	86.95% <100.00%> (+0.28%)	⬆️

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