[VM/Service] Fix profile_period_cli_option_test

I've seen up to 2500 samples get collected when running this test on
`vm-linux-debug-ia32` configs. 3000 is still significantly less than
5000, so this CL just changes the `lessThan(2000)` expectation to
`lessThan(3000)`.

Fixes: #60257
Change-Id: Iea88ec8dab6a3be9ca843bc445a8205730b8f2aa
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/414280
Reviewed-by: Jessy Yameogo <[email protected]>
Commit-Queue: Derek Xu <[email protected]>

Author: derekxu16

pkg/vm_service/test/profile_period_cli_option_test.dart

@@ -21,7 +21,7 @@ final tests = <IsolateTest>[
     // ms. So, we confirm that increasing the profile period using the CLI
     // option worked by confirming that we received significantly fewer than
     // 5000 samples.
-    expect(cpuSamples.sampleCount, lessThan(2000));
+    expect(cpuSamples.sampleCount, lessThan(3000));
   }
 ];