Fix dev container (#14906)

Co-authored-by: Travis Plunk <travis.plunk@microsoft.com>

.devcontainer/Dockerfile

@@ -3,7 +3,7 @@
 # Licensed under the MIT License. See https://go.microsoft.com/fwlink/?linkid=2090316 for license information.
 #-------------------------------------------------------------------------------------------------------------
 
-FROM mcr.microsoft.com/dotnet/nightly/sdk:6.0.100
+FROM mcr.microsoft.com/powershell/test-deps:ubuntu-18.04
 
 # Avoid warnings by switching to noninteractive
 ENV DEBIAN_FRONTEND=noninteractive

.devcontainer/devcontainer.json

@@ -1,6 +1,6 @@
 // See https://aka.ms/vscode-remote/devcontainer.json for format details.
 {
-	"name": ".NET Core 5.0, including pwsh (Debian 10)",
+	"name": ".NET Core 6.0, including pwsh (Ubuntu 18.04)",
 	"dockerFile": "Dockerfile",
 
 	// Uncomment the next line to run commands after the container is created.