test: tweak hydration mismatch test

Author: hi-ogawa

packages/plugin-rsc/e2e/basic.test.ts

@@ -994,16 +994,17 @@ function defineTest(f: Fixture) {
       errors.push(error)
     })
     await page.goto(f.url('/?test-hydration-mismatch'))
-    await waitForHydration(page)
-    expect(errors).toMatchObject([
-      {
-        message: expect.stringContaining(
-          f.mode === 'dev'
-            ? `Hydration failed because the server rendered HTML didn't match the client.`
-            : `Minified React error #418`,
-        ),
-      },
-    ])
+    await expect(() => {
+      expect(errors).toMatchObject([
+        {
+          message: expect.stringContaining(
+            f.mode === 'dev'
+              ? `Hydration failed because the server rendered HTML didn't match the client.`
+              : `Minified React error #418`,
+          ),
+        },
+      ])
+    }).toPass()
 
     errors.length = 0
     await page.goto(f.url())