Recommend Plone 6.1 Python versions for core development

Author: davisagli

docs/contributing/core/index.md

@@ -40,7 +40,7 @@ However, the following links and sections below may be helpful.
 ```{include} ../../volto/contributing/install-operating-system.md
 ```
 
--   Python {SUPPORTED_PYTHON_VERSIONS_PLONE60}
+-   Python {SUPPORTED_PYTHON_VERSIONS_PLONE61}
 -   {term}`GNU make`
 -   {term}`Git`
 -   A C compiler
@@ -50,7 +50,7 @@ However, the following links and sections below may be helpful.
 
 Installing Python is beyond the scope of this documentation.
 However, it is recommended to use a Python version manager, {term}`pyenv` that allows you to install multiple versions of Python on your development environment without destroying your system's Python.
-Plone requires Python version {SUPPORTED_PYTHON_VERSIONS_PLONE60}.
+Plone requires Python version {SUPPORTED_PYTHON_VERSIONS_PLONE61}.
 
 
 ### Make