announce the NumPy 2.3.1 release

Author: charris

content/en/news.md

@@ -461,6 +461,7 @@ Here is a list of NumPy releases, with links to release notes. Bugfix
 releases (only the `z` changes in the `x.y.z` version number) have no new
 features; minor releases (the `y` increases) do.
 
+- NumPy 2.3.1 ([release notes](https://github.com/numpy/numpy/releases/tag/v2.3.1)) -- _21 Jun 2025_.
 - NumPy 2.3.0 ([release notes](https://github.com/numpy/numpy/releases/tag/v2.3.0)) -- _7 Jun 2025_.
 - NumPy 2.2.6 ([release notes](https://github.com/numpy/numpy/releases/tag/v2.2.6)) -- _17 May 2025_.
 - NumPy 2.2.5 ([release notes](https://github.com/numpy/numpy/releases/tag/v2.2.5)) -- _19 Apr 2025_.