Update Dockerfile to support net9.0

Author: antoineatstariongroup

COMETwebapp/Dockerfile

@@ -16,7 +16,7 @@ RUN dotnet build COMETwebapp -c Release -o /app/build --no-restore
 FROM build AS publish
 RUN dotnet publish COMETwebapp -c Release -o /app/publish
 
-FROM mcr.microsoft.com/dotnet/aspnet:8.0.10-alpine3.20 AS final
+FROM mcr.microsoft.com/dotnet/aspnet:9.0.2-alpine3.21 AS final
 WORKDIR /app
 COPY --from=publish /app/publish .