Update main to use .NET SDK 9.0.311

This will align the bundled .NET binaries with those used in the next Seq 2025.2 patch, reducing compressed Docker image and MSI file sizes

Author: nblumhardt

ci.global.json

@@ -1,5 +1,5 @@
 {
   "sdk": {
-    "version": "9.0.306"
+    "version": "9.0.311"
   }
 }