Bump @angular/platform-server from 21.1.6 to 21.2.9 (#33333)

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Author: dependabot[bot]

apps/demos/package.json

@@ -90,7 +90,7 @@
         "express-rate-limit": "^8.3.1"
     },
     "devDependencies": {
-        "@angular/platform-server": "21.1.6",
+        "@angular/platform-server": "21.2.9",
         "@babel/core": "7.29.0",
         "@babel/eslint-parser": "catalog:",
         "@babel/preset-env": "7.29.0",