patch 8.2.4716: memory allocation failure not tested when defining a function

Problem:    Memory allocation failure not tested when defining a function.
Solution:   Add a test. (Yegappan Lakshmanan, closes #10127)

src/alloc.h

@@ -44,5 +44,6 @@ typedef enum {
     aid_newwin_wvars,
     aid_newtabpage_tvars,
     aid_blob_alloc,
+    aid_get_func,
     aid_last
 } alloc_id_T;