tests/basics/builtin_help.py: Test correct handling of deleted entries.

This test reproduces the bug that gave rise to the esp32 segfaults in
issues micropython#18061 and micropython#18481 on all platforms.

Signed-off-by: Anson Mansfield <amansfield@mantaro.com>

Author: AJMansfield

tests/basics/builtin_help.py

@@ -14,4 +14,10 @@
 help(micropython) # help for a module
 help('modules') # list available modules
 
+class A:
+    x = 1
+    y = 2
+    del x
+help(A)
+
 print('done') # so last bit of output is predictable