patch 8.2.1849: Vim9: garbage collection frees block-local variables

Problem:    Vim9: garbage collection frees block-local variables.
Solution:   Mark all script variables as used.
diff --git a/src/evalvars.c b/src/evalvars.c
index f325355..fd67ad0 100644
--- a/src/evalvars.c
+++ b/src/evalvars.c
@@ -303,12 +303,24 @@
     int
 garbage_collect_scriptvars(int copyID)
 {
-    int		i;
-    int		abort = FALSE;
+    int		    i;
+    int		    idx;
+    int		    abort = FALSE;
+    scriptitem_T    *si;
 
     for (i = 1; i <= script_items.ga_len; ++i)
+    {
 	abort = abort || set_ref_in_ht(&SCRIPT_VARS(i), copyID, NULL);
 
+	si = SCRIPT_ITEM(i);
+	for (idx = 0; idx < si->sn_var_vals.ga_len; ++idx)
+	{
+	    svar_T    *sv = ((svar_T *)si->sn_var_vals.ga_data) + idx;
+
+	    abort = abort || set_ref_in_item(sv->sv_tv, copyID, NULL, NULL);
+	}
+    }
+
     return abort;
 }