Upgrade our Devcontainer to Python 3.12 on Debian bookworm (#9580)

Author: cclauss

.devcontainer/Dockerfile

@@ -1,5 +1,5 @@
 # https://github.com/microsoft/vscode-dev-containers/blob/main/containers/python-3/README.md
-ARG VARIANT=3.11-bookworm
+ARG VARIANT=3.12-bookworm
 FROM mcr.microsoft.com/vscode/devcontainers/python:${VARIANT}
 COPY requirements.txt /tmp/pip-tmp/
 RUN python3 -m pip install --upgrade pip \

.devcontainer/README.md

@@ -0,0 +1 @@
+https://code.visualstudio.com/docs/devcontainers/tutorial

.devcontainer/devcontainer.json

@@ -4,10 +4,10 @@
 		"dockerfile": "Dockerfile",
 		"context": "..",
 		"args": {
-			// Update 'VARIANT' to pick a Python version: 3, 3.10, 3.9, 3.8, 3.7, 3.6
+			// Update 'VARIANT' to pick a Python version: 3, 3.11, 3.10, 3.9, 3.8
 			// Append -bullseye or -buster to pin to an OS version.
 			// Use -bullseye variants on local on arm64/Apple Silicon.
-			"VARIANT": "3.11-bookworm",
+			"VARIANT": "3.12-bookworm",
 		}
 	},