Fix: Main now is the future 3.15 not anymore 3.14

Followup of python/cpython#134649

Author: corneliusroemer

versions.rst

@@ -5,7 +5,7 @@
 Status of Python versions
 =========================
 
-The ``main`` branch is currently the future Python 3.14, and is the only
+The ``main`` branch is currently the future Python 3.15, and is the only
 branch that accepts new features.  The latest release for each Python
 version can be found on the `download page <https://www.python.org/downloads/>`_.