Fix race condition on metrics plugin E2E test

[jgwest]

What does this PR do / why we need it:

Fix this intermittent error in metrics E2E test:

------------------------------
• [FAILED] [22.256 seconds]
Namespace-scoped RolloutManager tests RolloutManager tests - namespace-scoped [It] Should add, update, and remove traffic and metric plugins through RolloutManager CR
/home/runner/work/argo-rollouts-manager/argo-rollouts-manager/tests/e2e/rollout_tests_all.go:600

  Timeline >>
  STEP: Verify that RolloutManager is successfully created. @ 10/31/24 08:09:26.89
  STEP: Verify traffic and metric plugin is added to ConfigMap @ 10/31/24 08:09:38.014
  STEP: Update traffic and metric plugins @ 10/31/24 08:09:38.019
  STEP: Get existing Rollouts Pod(s) before update @ 10/31/24 08:09:38.022
  STEP: Verify traffic and metric plugin is updated in ConfigMap @ 10/31/24 08:09:38.04
  STEP: Remove traffic and metric plugins @ 10/31/24 08:09:38.042
  STEP: Remove plugins from RolloutManager CR @ 10/31/24 08:09:38.044
  STEP: Verify that traffic and metric plugins are removed from ConfigMap @ 10/31/24 08:09:38.057
  STEP: Get existing Rollouts Pod(s) after update @ 10/31/24 08:09:39.062
  STEP: Verify Rollouts Pod is restarted @ 10/31/24 08:09:39.066
  [FAILED] in [It] - /home/runner/work/argo-rollouts-manager/argo-rollouts-manager/tests/e2e/rollout_tests_all.go:687 @ 10/31/24 08:09:39.077
  << Timeline

  [FAILED] Expected
      <[]v1.Pod | len:2, cap:2>: [
          {
              TypeMeta: {Kind: "", APIVersion: ""},
              ObjectMeta: {
                  Name: "argo-rollouts-ddccf95db-bw89k",
                  GenerateName: "argo-rollouts-ddccf95db-",
                  Namespace: "argo-rollouts",
                  SelfLink: "",
                  UID: "bfc185e8-7e42-474b-ab00-49aacb898e1f",
                  ResourceVersion: "3729",


(...)

  to have length 1
  In [It] at: /home/runner/work/argo-rollouts-manager/argo-rollouts-manager/tests/e2e/rollout_tests_all.go:687 @ 10/31/24 08:09:39.077
------------------------------

Have you updated the necessary documentation?

• Documentation update is required by this PR, and has been updated.

Which issue(s) this PR fixes:
Fixes #?

How to test changes / Special notes to the reviewer:

[Rizwana777]

Just added a minot comment, else LGTM

[jgwest]

Thanks @Rizwana777!