User buster-slim instead of non existent buster

deployment/Dockerfile.docker.amd64

@@ -1,6 +1,6 @@
 ARG DOTNET_VERSION=5.0
 
-FROM mcr.microsoft.com/dotnet/core/sdk:${DOTNET_VERSION}-buster
+FROM mcr.microsoft.com/dotnet/core/sdk:${DOTNET_VERSION}-buster-slim
 
 ARG SOURCE_DIR=/src
 ARG ARTIFACT_DIR=/jellyfin

deployment/Dockerfile.docker.arm64

@@ -1,6 +1,6 @@
 ARG DOTNET_VERSION=5.0
 
-FROM mcr.microsoft.com/dotnet/core/sdk:${DOTNET_VERSION}-buster
+FROM mcr.microsoft.com/dotnet/core/sdk:${DOTNET_VERSION}-buster-slim
 
 ARG SOURCE_DIR=/src
 ARG ARTIFACT_DIR=/jellyfin

deployment/Dockerfile.docker.armhf

@@ -1,6 +1,6 @@
 ARG DOTNET_VERSION=5.0
 
-FROM mcr.microsoft.com/dotnet/core/sdk:${DOTNET_VERSION}-buster
+FROM mcr.microsoft.com/dotnet/core/sdk:${DOTNET_VERSION}-buster-slim
 
 ARG SOURCE_DIR=/src
 ARG ARTIFACT_DIR=/jellyfin