[3.11] gh-100117: Fix inaccuracy in documentation of the CodeObject's…

… co_positions field. (GH-119364) (#119871)

(cherry picked from commit 015b1fd)

Co-authored-by: Irit Katriel <1055913+iritkatriel@users.noreply.github.com>

Doc/reference/datamodel.rst

@@ -1217,7 +1217,7 @@ Methods on code objects
 
    The iterator returns :class:`tuple`\s containing the ``(start_line, end_line,
    start_column, end_column)``. The *i-th* tuple corresponds to the
-   position of the source code that compiled to the *i-th* instruction.
+   position of the source code that compiled to the *i-th* code unit.
    Column information is 0-indexed utf-8 byte offsets on the given source
    line.