Fix flaky tests

[khanhtc1202]

What this PR does:

Why we need it:

Fix these flaky tests (in both kubernetes and kubernetes_multicluster plugins)
https://github.com/pipe-cd/pipecd/actions/runs/19011895918/job/54430014207?pr=6333#step:4:107

Which issue(s) this PR fixes:

Fixes #

Does this PR introduce a user-facing change?:

• How are users affected by this change:
• Is this breaking change:
• How to migrate (if breaking change):

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 28.83%. Comparing base (a2e18d7) to head (476dce3).
⚠️ Report is 37 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6334   +/-   ##
=======================================
  Coverage   28.83%   28.83%           
=======================================
  Files         560      560           
  Lines       59922    59922           
=======================================
  Hits        17277    17277           
  Misses      41324    41324           
  Partials     1321     1321           

Flag	Coverage Δ
.	23.28% <ø> (ø)
.-pkg-app-pipedv1-plugin-analysis	32.64% <ø> (ø)
.-pkg-app-pipedv1-plugin-kubernetes	58.54% <ø> (ø)
.-pkg-app-pipedv1-plugin-kubernetes_multicluster	67.63% <ø> (ø)
.-pkg-app-pipedv1-plugin-scriptrun	54.83% <ø> (ø)
.-pkg-app-pipedv1-plugin-terraform	38.65% <ø> (ø)
.-pkg-app-pipedv1-plugin-wait	33.92% <ø> (ø)
.-pkg-app-pipedv1-plugin-waitapproval	52.71% <ø> (ø)
.-pkg-plugin-sdk	50.34% <ø> (ø)
.-tool-actions-gh-release	19.23% <ø> (ø)
.-tool-actions-plan-preview	25.51% <ø> (ø)
.-tool-codegen-protoc-gen-auth	0.00% <ø> (ø)

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[Warashi]

👍🏻