gh-122245: Add test case of generic type with __debug__ (#122322)

Author: iritkatriel

Lib/test/test_syntax.py

@@ -2265,6 +2265,10 @@ def f(x: *b)
    Traceback (most recent call last):
    SyntaxError: cannot assign to __debug__
 
+   >>> class A[__debug__]: pass
+   Traceback (most recent call last):
+   SyntaxError: cannot assign to __debug__
+
    >>> class A[T]((x := 3)): ...
    Traceback (most recent call last):
       ...

Misc/NEWS.d/next/Core and Builtins/2024-07-24-22-39-07.gh-issue-122245.LVa9v8.rst

@@ -1,4 +1,4 @@
 Detection of writes to ``__debug__`` is moved from the compiler's codegen
-stage to the symtable. This means that these errors now detected even in
+stage to the symtable. This means that these errors are now detected even in
 code that is optimized away before codegen (such as assertions with the
-:option:`-O` command line option.)
+:option:`-O` command line option).