Fix #935 enterprise_id in InstallationQuery can be invalid for Slack Connect channel events

[seratch]

Summary

Refer to #935 for details. This is a critical bug for the non-Enterprise Grid customers using Slack Connect channels.

Requirements (place an x in each [ ])

• 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.

[codecov]

Codecov Report

Merging #949 (3a1aa3c) into main (0bb7ae9) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #949   +/-   ##
=======================================
  Coverage   66.19%   66.19%           
=======================================
  Files          13       13           
  Lines        1207     1207           
  Branches      356      356           
=======================================
  Hits          799      799           
  Misses        338      338           
  Partials       70       70           

Impacted Files	Coverage Δ
src/App.ts	82.91% <100.00%> (ø)

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[stevengill]

Great job debugging this and sending in the fix. It can be quite challenging even reproducing these complicated cases.