Updates the commit we run the `material-unit-tests` job
against. The latest commit includes https://github.com/angular/components/commit/1255139a38e5d8425bb6236c63c3d231301b21da

This commit reduces the flakiness of a `MatMenu` test and therefore
improves the stability of the material-unit-tests job.

Example failing build: https://circleci.com/gh/angular/angular/521625

PR Close #33716