use a base image with .NET 9 installed

Author: atoulme

packaging/tests/deb/dotnet/Dockerfile

@@ -8,7 +8,7 @@ RUN dotnet build "DotNetTestApp.csproj" -c Release -o /app/build
 FROM build AS publish
 RUN dotnet publish "DotNetTestApp.csproj" -c Release -o /app/publish
 
-FROM debian:12 AS final
+FROM mcr.microsoft.com/dotnet/runtime:9.0-bookworm-slim AS final
 
 ARG ARCH=amd64
 ARG RPM_ARCH=x86_64
@@ -18,14 +18,6 @@ ENV LANG=C.UTF-8
 RUN apt-get update
 RUN apt install -y  wget
 
-RUN wget https://packages.microsoft.com/config/debian/12/packages-microsoft-prod.deb -O packages-microsoft-prod.deb && \
-    dpkg -i packages-microsoft-prod.deb && \
-    rm packages-microsoft-prod.deb
-
-RUN apt-get update
-
-RUN apt-get install -y dotnet-runtime-9.0 dotnet-sdk-9.0
-
 # TODO The otel collector version needs to be kept up to date, potentially with renovate.
 RUN wget https://github.com/open-telemetry/opentelemetry-collector-releases/releases/download/v0.128.0/otelcol-contrib_0.128.0_linux_${ARCH}.deb
 RUN dpkg -i otelcol-contrib_0.128.0_linux_${ARCH}.deb