Upgrade .NET version to 9.0 in Dockerfile, devcontainer.json, build.yml, and global.json

Author: Arlodotexe

.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:9.0
 
 # [Choice] Node.js version: none, lts/*, 16, 14, 12, 10
 ARG NODE_VERSION="none"

.devcontainer/devcontainer.json

@@ -7,7 +7,7 @@
 		"args": {
 			// Update 'VARIANT' to pick a .NET Core version: 3.1, 5.0, 6.0
 			// Append -bullseye or -focal to pin to an OS version.
-			"VARIANT": "8.0",
+			"VARIANT": "9.0",
 			// Options
 			"NODE_VERSION": "lts/*"
 		}

.github/workflows/build.yml

@@ -16,9 +16,7 @@ on:
   workflow_dispatch:
 
 env:
-  DOTNET_VERSION: ${{ '8.0.x' }}
-  DOTNET_INSTALL_DIR: dotnet-install
-  DOTNET_ROOT: dotnet-install
+  DOTNET_VERSION: ${{ '9.0.x' }}
   ENABLE_DIAGNOSTICS: false
   #COREHOST_TRACE: 1
   COREHOST_TRACEFILE: corehosttrace.log

global.json

@@ -1,6 +1,6 @@
 {
   "sdk": {
-    "version": "8.0.403",
+    "version": "9.0.101",
     "rollForward": "latestFeature"
   },
   "msbuild-sdks":