Updated to .NET 9

Author: whyvra

Dockerfile

@@ -11,11 +11,11 @@ RUN curl -O https://packages.microsoft.com/config/debian/11/packages-microsoft-p
     && apt-get update \
     && apt-get install -y apt-transport-https libgdiplus libc6-dev \
     && apt-get update \
-    && apt-get install -y dotnet-sdk-8.0 \
+    && apt-get install -y dotnet-sdk-9.0 \
     && apt-get install -y -t bullseye-backports git \
     && apt-get clean \
     && rm -rf /var/lib/apt/lists/*
 
 USER 1000
 
-ENV DOTNET_CLI_TELEMETRY_OPTOUT=1
+ENV DOTNET_CLI_TELEMETRY_OPTOUT=1