[gh-1349] Update branch build to .NET 9

Author: ashmind

#scripts/roslyn-branches/arm/template.json

@@ -34,7 +34,7 @@
                 "serverFarmId": "[variables('serverfarms_main_id')]",
                 "clientAffinityEnabled": false,
                 "siteConfig": {
-                    "netFrameworkVersion": "v8.0",
+                    "netFrameworkVersion": "v9.0",
                     "publishingUsername": "[concat('$', parameters('sites_name'))]",
                     "use32BitWorkerProcess": true,
                     "webSocketsEnabled": true,

#scripts/roslyn-branches/flow/update/updateBranch.ts

@@ -242,7 +242,7 @@ async function buildSharpLab(roslynPackagesRoot: string) {
     });
 
     return {
-        publishRoot: `${branchSourceRoot}/Server/bin/Release/net8.0/publish`
+        publishRoot: `${branchSourceRoot}/Server/bin/Release/net9.0/publish`
     };
 }