test: fix timezone for tests (#7389)

Author: andyjessop

fixtures/vitest-pool-workers-examples/vitest.global.ts

@@ -0,0 +1,3 @@
+export function setup(): void {
+	process.env.TZ = "UTC";
+}

fixtures/vitest-pool-workers-examples/vitest.workers.config.ts

@@ -14,6 +14,7 @@ class FilteredPushArray<T> extends Array<T> {
 
 export default defineConfig({
 	test: {
+		globalSetup: ["./vitest.global.ts"],
 		// Configure the `vite-node` server used by Vitest code to import configs,
 		// custom pools and tests. By default, Vitest effectively applies Vite
 		// transforms to all files outside `node_modules`. This means by default,