chore: update releases

Author: alanpoulain

extra/releases.md

@@ -6,7 +6,7 @@ A new minor version is released every six months, and a new major version is rel
 For example:
 
 - version 3.0 has been released on 15 September, 2022;
-- version 3.1 will be released on March, 2023;
+- version 3.1 has been released on 23 January, 2023;
 - version 3.2 will be released on September, 2023;
 - version 3.3 will be released on March, 2024;
 - versions 3.4 and 4.0 will be released on September, 2024.
@@ -15,11 +15,11 @@ For example:
 
 3 versions are maintained at the same time:
 
-* **stable** (currently the **3.0** branch): regular bugfixes are integrated in this version
-* **old-stable** (currently **2.7** branch): [security fixes](security.md) are integrated in this version, regular bugfixes are **not** backported in it
+* **stable** (currently the **3.1** branch): regular bugfixes are integrated in this version
+* **old-stable** (currently **3.0** branch): [security fixes](security.md) are integrated in this version, regular bugfixes are **not** backported in it
 * **development** (**main** branch): new features target this branch
 
-Older versions (1.x, 2.6...) **are not maintained**. If you still use them, you must upgrade as soon as possible.
+Older versions (1.x, 2.7...) **are not maintained**. If you still use them, you must upgrade as soon as possible.
 
 The **old-stable** branch is merged in the **stable** branch on a regular basis to propagate [security fixes](security.md).
 The **stable** branch is merged in the **development** branch on a regular basis to propagate [security](security.md) and regular bugfixes.