Remove hardcoded line number references from test comments

[Copilot]

• Resolves: add postinstall event #179 (code review feedback)

Summary

Line number references in test comments become stale as code evolves. Removed all hardcoded line numbers from SetupTest.php and replaced with descriptive text.

Changes

• Helper method comment: Replaced references to lines 329, 502-503, 321-323 with general descriptions
• Test method docblock: Removed line 329 and 502-503 references, described logic conceptually
• Inline comment: Replaced line 504-506 reference with behavior description

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone added for target branch/version (ex: 32.x for stable32)

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