tests/misc/sys_settrace_features.py: Add note about CPython 3.12 issue.

CPython 3.12 has a documented issue with settrace for opcodes, apparently
due to PEP 669.  "This behavior will be changed back in 3.13 to be
consistent with previous versions."

No easy way to make the test pass on CPython 3.12, but at least this helps
signal what the problem is to anyone who runs into a failure.

This work was funded through GitHub Sponsors.

Signed-off-by: Angus Gratton <angus@redyak.com.au>

tests/misc/sys_settrace_features.py

@@ -6,6 +6,10 @@ except AttributeError:
     print("SKIP")
     raise SystemExit
 
+if sys.version.startswith("3.12"):
+    # There is a CPython change in settrace that is reverted in 3.13!
+    print("WARNING: this test will fail when compared to CPython 3.12.x behaviour")
+
 
 def print_stacktrace(frame, level=0):
     # Ignore CPython specific helpers.