docs: clarify trace function implementation used by default depending on the Python version

Author: mschoettle

doc/config.rst

@@ -335,8 +335,9 @@ Before version 4.2, this option only accepted a single string.
 
 (string) Specify which trace function implementation to use. Valid values are:
 "pytrace" for the pure Python implementation, "ctrace" for the C implementation
-(default), or "sysmon" for the :mod:`sys.monitoring <python:sys.monitoring>`
-implementation (Python 3.12+ only).
+(default until Python 3.13),
+or "sysmon" for the :mod:`sys.monitoring <python:sys.monitoring>`
+implementation (default with Python 3.14+).
 
 This was previously only available as the COVERAGE_CORE environment variable.
 Note that the "sysmon" core does not yet support plugins or dynamic contexts.