patch 8.2.4573: a nested function is compiled for debugging without context

Problem:    A nested function (closure) is compiled for debugging without
            context.
Solution:   Check if a nested function is marked for debugging before
            compiling it.  Give an error when trying to compile a closure
            without its context. (closes #9951)
diff --git a/src/vim9execute.c b/src/vim9execute.c
index 2cf7e46..681847a 100644
--- a/src/vim9execute.c
+++ b/src/vim9execute.c
@@ -152,7 +152,7 @@
  * If debug_tick changed check if "ufunc" has a breakpoint and update
  * "uf_has_breakpoint".
  */
-    static void
+    void
 update_has_breakpoint(ufunc_T *ufunc)
 {
     if (ufunc->uf_debug_tick != debug_tick)