Add boundary test cases for statusClass

Bob Singhrequested to merge
bobsingh.dev/gitlab-runner-deletion_scheduled-77678126:test-status-class-boundaries into main

What does this MR do? Adds boundary test coverage for statusClass by checking out-of-range lower and upper values and the highest valid 5xx status.

Why was this MR needed? Improves test coverage for boundary conditions and helps ensure status classification behaves correctly for edge-case inputs.

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