Update dependency nextra to v4.3.0-alpha.20

Author: renovate[bot]

apps/docs/package.json

@@ -39,7 +39,7 @@
     "classix": "2.2.2",
     "comment-parser": "1.4.1",
     "next": "15.3.0",
-    "nextra": "4.3.0-alpha.18",
+    "nextra": "4.3.0-alpha.20",
     "nextra-theme-docs": "4.2.17",
     "react": "19.1.0",
     "react-dom": "19.1.0",