Updated dotnet container to 8.0

.devcontainer/Dockerfile

@@ -1,8 +1,5 @@
-# See here for image contents: https://github.com/microsoft/vscode-dev-containers/tree/v0.208.0/containers/dotnet/.devcontainer/base.Dockerfile
-
-# [Choice] .NET version: 6.0, 5.0, 3.1, 6.0-bullseye, 5.0-bullseye, 3.1-bullseye, 6.0-focal, 5.0-focal, 3.1-focal
-ARG VARIANT="6.0-bullseye-slim"
-FROM mcr.microsoft.com/vscode/devcontainers/dotnet:0-${VARIANT}
+# See https://github.com/devcontainers/images/tree/main/src/dotnet for image choices
+FROM mcr.microsoft.com/vscode/devcontainers/dotnet:8.0
 
 # [Choice] Node.js version: none, lts/*, 16, 14, 12, 10
 ARG NODE_VERSION="none"