tests/cpydiff: Update CPy diff for assign expr in nested comprehensions.

Since 7c1584a MicroPython matches CPython in most cases, aside from
nested comprehensions.

This work was funded through GitHub Sponsors.

Signed-off-by: Angus Gratton <[email protected]>

Author: projectgus

tests/cpydiff/syntax_assign_expr.py

@@ -1,8 +1,8 @@
 """
 categories: Syntax,Operators
-description: MicroPython allows using := to assign to the variable of a comprehension, CPython raises a SyntaxError.
-cause: MicroPython is optimised for code size and doesn't check this case.
-workaround: Do not rely on this behaviour if writing CPython compatible code.
+description: MicroPython allows := to assign to the iteration variable in nested comprehensions, CPython does not.
+cause: MicroPython is optimised for code size. Although it is a syntax error to assign to the iteration variable in a standard comprehension (same as CPython), it doesn't check if an inner nested comprehension assigns to the iteration variable of the outer comprehension.
+workaround: Do not use := to assign to the iteration variable of a comprehension.
 """
 
-print([i := -1 for i in range(4)])
+print([[(j := i) for i in range(2)] for j in range(2)])