patch 8.2.1012: Vim9: cannot declare single character script variables

Problem:    Vim9: cannot declare single character script variables.
Solution:   Don't see "b:", "s:", etc. as namespace.  Fix item size of
            sn_var_vals.
diff --git a/src/scriptfile.c b/src/scriptfile.c
index 746a3d3..abfa3b5 100644
--- a/src/scriptfile.c
+++ b/src/scriptfile.c
@@ -1343,7 +1343,7 @@
 
 	    // Allocate the local script variables to use for this script.
 	    new_script_vars(script_items.ga_len);
-	    ga_init2(&si->sn_var_vals, sizeof(typval_T), 10);
+	    ga_init2(&si->sn_var_vals, sizeof(svar_T), 10);
 	    ga_init2(&si->sn_imports, sizeof(imported_T), 10);
 	    ga_init2(&si->sn_type_list, sizeof(type_T), 10);
 # ifdef FEAT_PROFILE