gh-132346: Docs: Clarify that reference counts aren't stable between versions (GH-132352)

(cherry picked from commit 3dbe02c)

Co-authored-by: Peter Bierma <zintensitydev@gmail.com>

Author: ZeroIntensity

Doc/glossary.rst

@@ -1163,6 +1163,11 @@ Glossary
       :func:`sys.getrefcount` function to return the
       reference count for a particular object.
 
+      In :term:`CPython`, reference counts are not considered to be stable
+      or well-defined values; the number of references to an object, and how
+      that number is affected by Python code, may be different between
+      versions.
+
    regular package
       A traditional :term:`package`, such as a directory containing an
       ``__init__.py`` file.