chore: Limit tests concurrency (#304)

vite.config.e2e-functional.mjs

@@ -1,5 +1,6 @@
 // Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
 // SPDX-License-Identifier: Apache-2.0
+import os from "node:os";
 import { defineConfig } from "vite";
 import base from "./vite.config.mjs";
 
@@ -13,5 +14,12 @@ export default defineConfig({
     include: ["./test/functional/**/*.test.ts"],
     setupFiles: ["./test/test-setup.ts"],
     globalSetup: ["./test/global-setup.ts"],
+    poolOptions: {
+      threads: {
+        minThreads: 1,
+        // leave half of CPU capacity for Chrome browser processes
+        maxThreads: Math.max(Math.floor(os.cpus().length / 2), 1),
+      },
+    },
   },
 });