chore(deps): update dependency vitepress to v1.0.0-alpha.21 (#1461)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>
Co-authored-by: ST-DDT <ST-DDT@gmx.de>

Author: renovate[bot]

package.json

@@ -135,7 +135,7 @@
     "typescript": "~4.8.4",
     "validator": "~13.7.0",
     "vite": "~3.1.7",
-    "vitepress": "1.0.0-alpha.19",
+    "vitepress": "1.0.0-alpha.21",
     "vitest": "~0.24.1"
   },
   "packageManager": "pnpm@7.13.4",