Mention Python 3.13 venv gitignore behavior

Python 3.13's venv module creates SCM ignore files by default, including Git ignore files, so the manual .gitignore step is only needed for Python 3.12 and below.

This matches the existing uv tip, as uv also creates .venv/.gitignore when creating the virtual environment.

Reference: https://docs.python.org/3/whatsnew/3.13.html#venv

Context: noticed while checking virtual-environments.md after fastapi#15463 in 0.163.2.

Author: ftnext

docs/en/docs/virtual-environments.md

@@ -268,6 +268,12 @@ If you are using **Git** (you should), add a `.gitignore` file to exclude everyt
 
 /// tip
 
+If you used Python 3.13 or newer, it already did this for you, you can skip this step. 😎
+
+///
+
+/// tip
+
 If you used [`uv`](https://github.com/astral-sh/uv) to create the virtual environment, it already did this for you, you can skip this step. 😎
 
 ///