Update .NET 9 URLs to maintenance status

Author: lbussell

manifest.versions.json

@@ -80,8 +80,8 @@
     "dotnet|9.0|product-version": "9.0.1",
     "dotnet|9.0|fixed-tag": "$(dotnet|9.0|product-version)",
     "dotnet|9.0|minor-tag": "9.0",
-    "dotnet|9.0|base-url|main": "$(base-url|public|preview|main)",
-    "dotnet|9.0|base-url|nightly": "$(base-url|public|preview|nightly)",
+    "dotnet|9.0|base-url|main": "$(base-url|public|maintenance|main)",
+    "dotnet|9.0|base-url|nightly": "$(base-url|public|maintenance|nightly)",
 
     "libicu|bookworm": 72,
     "libicu|bullseye": 67,
@@ -123,7 +123,7 @@
     "monitor|9.0|fixed-tag": "$(monitor|9.0|product-version)",
     "monitor|9.0|minor-tag": "9.0",
     "monitor|9|major-tag": "9",
-    "monitor|9.0|base-url|main": "$(base-url|public|preview|main)",
+    "monitor|9.0|base-url|main": "$(base-url|public|maintenance|main)",
     "monitor|9.0|base-url|nightly": "$(base-url|public|preview|nightly)",
     "monitor-base|9.0|linux|x64|sha": "8ab4755e561e052f0ad4e1bbd20fb8f254fd4adc7b700d8f6a7a2472ff6d5bf9a7632ac0118cd0ef3b70587360a60975c7b44fbcca5e5655dfa2db225075ce4f",
     "monitor-base|9.0|linux|arm64|sha": "a3d6971bf58cf7db5498326a62dccf9aa25e85c2eb82b65148626c69406d11ab51dad9e49081b73a1eefbfed5396baf026148f73811be53579657e59994e7aff",