Robustify MenuItem label/accel tests

Editor assessment

The subject names the effort, making MenuItem label and accelerator tests more robust, and the body's bullets supply the specifics: truthy assertion checks were corrected and boolean-assert messages properly set, which are concrete defects rather than vague claims. The test type fits, no scope is attached, and no footers appear. Hygiene is acceptable, with the coined verb robustify slightly informal but clear. The message communicates both the affected tests and the nature of their unreliability, which gives readers genuine diagnostic context rather than a bare activity report.