patch 8.2.2170: Vim9: a global function defined in a :def function fails

Problem:    Vim9: a global function defined in a :def function fails if it
            uses the context.
Solution:   Create a partial to store the closure context. (see #7410)
diff --git a/src/proto/userfunc.pro b/src/proto/userfunc.pro
index 0029dab..787d010 100644
--- a/src/proto/userfunc.pro
+++ b/src/proto/userfunc.pro
@@ -13,7 +13,7 @@
 ufunc_T *find_func(char_u *name, int is_global, cctx_T *cctx);
 int func_is_global(ufunc_T *ufunc);
 int func_name_refcount(char_u *name);
-void copy_func(char_u *lambda, char_u *global);
+ufunc_T *copy_func(char_u *lambda, char_u *global);
 int funcdepth_increment(void);
 void funcdepth_decrement(void);
 int funcdepth_get(void);