patch 8.2.0650: Vim9: script function can be deleted

Problem:    Vim9: script function can be deleted.
Solution:   Disallow deleting script function.  Delete functions when sourcing
            a script again.
diff --git a/src/testing.c b/src/testing.c
index 35c2683..604d39b 100644
--- a/src/testing.c
+++ b/src/testing.c
@@ -789,7 +789,7 @@
 	    {
 		ufunc_T *fp;
 
-		fp = find_func(argvars[0].vval.v_string, NULL);
+		fp = find_func(argvars[0].vval.v_string, FALSE, NULL);
 		if (fp != NULL)
 		    retval = fp->uf_refcount;
 	    }