Fix type consistency in for_each empty set handling

[Copilot]

Addresses feedback from #2 about type consistency in conditional for_each expressions.

Changes

• Updated data.github_user.referenced_users and data.github_app.bypass_apps to use toset([]) instead of [] in the false branch of ternary operators
• Ensures both branches return consistent set types for for_each, which expects set or map

# Before
for_each = length(var.github_user_ids) == 0 ? toset(local.all_user_logins) : []

# After
for_each = length(var.github_user_ids) == 0 ? toset(local.all_user_logins) : toset([])

While Terraform coerces empty lists in practice, explicit type matching improves clarity and avoids potential edge cases.

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