gh-100117: Fix inaccuracy in documentation of the CodeObject's co_positions field. (#119364)

Author: iritkatriel

Doc/reference/datamodel.rst

@@ -1243,7 +1243,7 @@ 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.