migrating-to-v5: fix broken links to dependency-injection page
migrating-to-v5: fix broken links to dependency-injection page

The DI page was renamed: `di.md` -> `dependency-injection.md`.

cc @kwalrath

Closes #1650

PiperOrigin-RevId: 219371649

matanlurey/angular,matanlurey/angular,matanlurey/angular,angulardart/angular,angulardart/angular,angulardart/angular