Update to .NET 9.0: global.json and Dockerfile changes

Co-authored-by: BenjaminMichaelis <[email protected]>

Author: Copilot

EssentialCSharp.Web/Dockerfile

@@ -5,7 +5,7 @@ WORKDIR /app
 EXPOSE 8080
 EXPOSE 8081
 
-FROM mcr.microsoft.com/dotnet/sdk:9.0.305 AS build
+FROM mcr.microsoft.com/dotnet/sdk:9.0 AS build
 ARG ACCESS_TO_NUGET_FEED=true
 ENV ACCESS_TO_NUGET_FEED=$ACCESS_TO_NUGET_FEED
 RUN sh -c "$(curl -fsSL https://aka.ms/install-artifacts-credprovider.sh)"

global.json

@@ -1,6 +1,6 @@
 {
   "sdk": {
-    "version": "9.0.101",
-    "rollForward": "latestMinor"
+    "version": "9.0.100",
+    "rollForward": "latestPatch"
   }
 }