test: fix race condition in serverComponentsHmrCache tests (#70368)

fixes a race condition in the `after()`-related test in
`server-components-hmr-cache.test.ts`

i made `getLoggedAfterValue` stricter while investigating an unrelated
issue, and saw it occasionally throw (see [CI
run](https://github.com/vercel/next.js/actions/runs/11001754094/job/30547234764?pr=70362#step:29:708)).
before this change, if `getLoggedAfterValue` was called before any logs
with `"After: "` were written, it would just return `undefined`, which
is obviously not what the test wants. this seems to have been happening
occasionally, but it wasn't visible because even if we got `undefined`
from one of the calls, the
`expect(valueBeforePatch).not.toEqual(valueAfterPatch)` assertion would
still pass -- one of the values is a string and the other is
`undefined`, so obviously they're not equal!

test/development/app-dir/server-components-hmr-cache/server-components-hmr-cache.test.ts

@@ -6,8 +6,16 @@ describe('server-components-hmr-cache', () => {
   const loggedAfterValueRegexp = /After: (\d\.\d+)/
   let cliOutputLength: number
 
-  const getLoggedAfterValue = () =>
-    next.cliOutput.slice(cliOutputLength).match(loggedAfterValueRegexp)?.[1]
+  const getLoggedAfterValue = () => {
+    const match = next.cliOutput
+      .slice(cliOutputLength)
+      .match(loggedAfterValueRegexp)
+
+    if (!match) {
+      throw new Error('No logs from after() found')
+    }
+    return match[1]
+  }
 
   describe.each(['edge', 'node'])('%s runtime', (runtime) => {
     afterEach(async () => {
@@ -124,7 +132,7 @@ describe('server-components-hmr-cache', () => {
 
         it('should not use cached fetch calls for fast refresh requests', async () => {
           const browser = await next.browser(`/${runtime}`)
-          const valueBeforePatch = getLoggedAfterValue()
+          const valueBeforePatch = await retry(() => getLoggedAfterValue())
           cliOutputLength = next.cliOutput.length
 
           await next.patchFile('components/shared-page.tsx', (content) =>
@@ -136,7 +144,7 @@ describe('server-components-hmr-cache', () => {
             expect(updatedContent).toBe('bar')
           })
 
-          const valueAfterPatch = getLoggedAfterValue()
+          const valueAfterPatch = await retry(() => getLoggedAfterValue())
           expect(valueBeforePatch).not.toEqual(valueAfterPatch)
         })
       })