[ci]: de-flake client cache test (#84517)

Waits for prefetches to complete before navigating.
[x-ref](https://github.com/vercel/next.js/actions/runs/18237285313/attempts/3)

Author: ztanner

test/e2e/app-dir/app-client-cache/client-cache.experimental.test.ts

@@ -75,6 +75,9 @@ describe('app dir client cache semantics (experimental staleTimes)', () => {
       it('should re-use the cache for 5 minutes (default "static" time)', async () => {
         const browser = await next.browser('/', browserConfigWithFixedTime)
 
+        // Wait for the prefetch to complete before clicking
+        await browser.waitForIdleNetwork()
+
         let initialRandomNumber = await browser
           .elementByCss('[href="/0?timeout=0"]')
           .click()
@@ -265,6 +268,9 @@ describe('app dir client cache semantics (experimental staleTimes)', () => {
       it('should use the custom static override time (3 minutes)', async () => {
         const browser = await next.browser('/', browserConfigWithFixedTime)
 
+        // Wait for the prefetch to complete before clicking
+        await browser.waitForIdleNetwork()
+
         let initialRandomNumber = await browser
           .elementByCss('[href="/0?timeout=0"]')
           .click()