dep: bump vitepress from 1.0.0-alpha.27 to 1.0.0-alpha.28

Can't show this merge request because the source branch dependabot-npm_and_yarn-vitepress-1.0.0-alpha.28 is missing from project georgekoltsov-multiple-projects-test-4/imported-project-ef029319134ab099. Close this merge request or update the source branch.