Strengthen test assertions in llm_gateway_test.go using jsonPointerGet

[yrobla]

Summary

Tests in pkg/client/llm_gateway_test.go were using assert.Contains on raw file bytes, which passes even when a value lands at the wrong JSON pointer or appears only as a key name. This extends the jsonPointerGet-based assertion pattern (introduced in #5142) to all remaining tests in the file.

• Replace raw-string assert.Contains with jsonPointerGet exact-path assertions in TestConfigureLLMGateway_CreatesFile, _DeepNestedKey, _PreservesExistingKeys, _ProxyMode, and the three TLS skip-verify tests
• Replace assert.NotContains with _, ok := jsonPointerGet(...); assert.False(t, ok) in TestRevertLLMGateway_RemovesKey and the TLS / Gemini TLS tests
• assert.Contains is kept where jsonPointerGet cannot help: JSONC comment preservation checks and non-string JSON values (e.g. the permissions object)

Fixes #5179

Type of change

• Bug fix
• New feature
• Refactoring (no behavior change)
• Dependency update
• Documentation
• Other (describe):

Test plan

• Unit tests (task test)
• E2E tests (task test-e2e)
• Linting (task lint-fix)
• Manual testing (describe below)

API Compatibility

• This PR does not break the v1beta1 API, OR the api-break-allowed label is applied and the migration guidance is described above.

Changes

File	Change

Does this introduce a user-facing change?

Implementation plan

Approved implementation plan

Special notes for reviewers

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 67.57%. Comparing base (655de22) to head (287d0e0).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5187      +/-   ##
==========================================
+ Coverage   67.53%   67.57%   +0.03%     
==========================================
  Files         602      602              
  Lines       61167    61167              
==========================================
+ Hits        41310    41334      +24     
+ Misses      16729    16704      -25     
- Partials     3128     3129       +1     

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[Copilot]

Pull request overview

This PR strengthens the correctness of pkg/client/llm_gateway_test.go by replacing brittle raw-substring assertions against the serialized settings file with exact JSON-pointer lookups via jsonPointerGet, ensuring tests fail when values land at the wrong path (or only appear as key names).

Changes:

• Replaced multiple assert.Contains(string(data), ...) checks with jsonPointerGet(data, "/path") + assert.Equal(...) for exact JSON-pointer assertions.
• Replaced several assert.NotContains(...) checks with jsonPointerGet(...); assert.False(t, ok) in revert and TLS-related tests.
• Kept raw-substring assertions where the asserted value is non-string JSON (e.g., permissions) or where JSONC comment preservation is being tested.

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