test: fix luacheck warnings in test/wal_off

Closes #5467

Reviewed-by: Vladislav Shpilevoy <v.shpilevoy@tarantool.org>
Reviewed-by: Igor Munkin <imun@tarantool.org>

Co-authored-by: Vladislav Shpilevoy <v.shpilevoy@tarantool.org>
Co-authored-by: Igor Munkin <imun@tarantool.org>

.luacheckrc

@@ -45,7 +45,7 @@ exclude_files = {
     "test/swim/**/*.lua",
     "test/var/**/*.lua",
     "test/vinyl/**/*.lua",
-    "test/wal_off/**/*.lua",
+    "test/wal_off/*.test.lua",
     "test/xlog/*.test.lua",
     "third_party/**/*.lua",
     ".rocks/**/*.lua",