test: use pool threads to mitigate onTaskUpdate error

Author: velut

vitest.config.ts

@@ -2,6 +2,7 @@ import { defineConfig } from "vitest/config";
 
 export default defineConfig({
 	test: {
+		pool: "threads",
 		testTimeout: 60_000, // Analyzing npm packages takes time.
 		coverage: { include: ["src/**"] },
 	},