fix: test instability in UpdateCACertToClusterInterceptorCRD unit test

[l-qing]

• Add proper cleanup mechanism for the ticker goroutine in UpdateCACertToClusterInterceptorCRD
• Return a stop function to allow graceful shutdown of the background goroutine
• Update caller to use the returned stop function and handle the return value
• Add defer statement in test to ensure proper cleanup

Changes

Fix test instability in UpdateCACertToClusterInterceptorCRD unit test

This PR addresses test instability issues in the Test_UpdateCACertToClusterInterceptorCRD unit test by improving resource cleanup in the tested function.

panic: Log in goroutine after Test_UpdateCACertToClusterInterceptorCRD has completed: 2025-08-13T02:15:36.599Z	ERROR	failed to fetch secret secret "testsecrets" not found

goroutine 26 [running]:
testing.(*common).logDepth(0xc00098e700, {0xc00055d920, 0x54}, 0x3)
	/target/usr/local/go/src/testing/testing.go:1064 +0x4b4
testing.(*common).log(...)
	/target/usr/local/go/src/testing/testing.go:1046
testing.(*common).Logf(0xc00098e700, {0x2e5f996?, 0x400?}, {0xc000487570?, 0x2?, 0x1?})
	/target/usr/local/go/src/testing/testing.go:1097 +0x54
go.uber.org/zap/zaptest.TestingWriter.Write({{0x325fbb0?, 0xc00098e700?}, 0xc0?}, {0xc0001f2c00?, 0x55, 0xc0001f2c00?})
	/workspace/source/upstream/vendor/go.uber.org/zap/zaptest/logger.go:146 +0xdb
go.uber.org/zap/zapcore.(*ioCore).Write(0xc000593d40, {0x2, {0xc21f1b3223b5b9a1, 0x4b06b72d6, 0x4f8a160}, {0x0, 0x0}, {0xc00054db40, 0x35}, {0x0, ...}, ...}, ...)
	/workspace/source/upstream/vendor/go.uber.org/zap/zapcore/core.go:99 +0xb5
go.uber.org/zap/zapcore.(*CheckedEntry).Write(0xc00037f1e0, {0x0, 0x0, 0x0})
	/workspace/source/upstream/vendor/go.uber.org/zap/zapcore/entry.go:253 +0x119
go.uber.org/zap.(*SugaredLogger).log(0xc000800ae0, 0x2, {0x2e83532?, 0x19?}, {0xc000729fc0?, 0x1?, 0x1?}, {0x0, 0x0, 0x0})
	/workspace/source/upstream/vendor/go.uber.org/zap/sugar.go:355 +0xec
go.uber.org/zap.(*SugaredLogger).Errorf(...)
	/workspace/source/upstream/vendor/go.uber.org/zap/sugar.go:216
github.com/tektoncd/triggers/pkg/interceptors/server.UpdateCACertToClusterInterceptorCRD.func1()
	/workspace/source/upstream/pkg/interceptors/server/server.go:335 +0x25b
created by github.com/tektoncd/triggers/pkg/interceptors/server.UpdateCACertToClusterInterceptorCRD in goroutine 25
	/workspace/source/upstream/pkg/interceptors/server/server.go:330 +0x13b

FAIL	github.com/tektoncd/triggers/pkg/interceptors/server	20.154s

Problem:

• The unit test was occasionally failing due to improper resource cleanup
• Background goroutines and tickers from the UpdateCACertToClusterInterceptorCRD function weren't being properly stopped after test completion
• This caused test interference and flaky test results

Solution:

• Modified UpdateCACertToClusterInterceptorCRD to return a cleanup function
• Added proper goroutine termination mechanism using a done channel and select statement
• Ensured ticker is properly stopped with defer ticker.Stop()
• Updated the test to call the cleanup function, ensuring proper test isolation

Submitter Checklist

As the author of this PR, please check off the items in this checklist:

• Has Docs if any changes are user facing, including updates to minimum requirements e.g. Kubernetes version bumps
• Has Tests included if any functionality added or changed
• Follows the commit message standard
• Meets the Tekton contributor standards (including functionality, content, code)
• Has a kind label. You can add one by adding a comment on this PR that contains /kind <type>. Valid types are bug, cleanup, design, documentation, feature, flake, misc, question, tep
• Release notes block below has been updated with any user facing changes (API changes, bug fixes, changes requiring upgrade notices or deprecation warnings). See some examples of good release notes.
• Release notes contains the string "action required" if the change requires additional action from users switching to the new release

Release Notes

NONE

/kind flake

[tekton-robot]

The following is the coverage report on the affected files.
Say /test pull-tekton-triggers-go-coverage to re-run this coverage report

File	Old Coverage	New Coverage	Delta
pkg/interceptors/server/server.go	Do not exist	81.5%

[khrm]

/retest

[tekton-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: savitaashture

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [savitaashture]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[savitaashture]

/lgtm