refactor(github): use Octokit REST namespace

[grolu]

How to categorize this PR?

/area dev-productivity
/kind cleanup

What this PR does / why we need it:

Migrates the GitHub integration from Octokit's legacy root-level REST methods to the octokit.rest namespace. This removes reliance on the compatibility API while preserving the existing issue search, update, and comment behavior.

Which issue(s) this PR fixes:

None.

Special notes for your reviewer:

This follows the Octokit major update from #3146. The full pre-push verification completed successfully.

Release note:

NONE

Summary by CodeRabbit

• Bug Fixes
  • Improved GitHub issue search, retrieval, updates, and comment creation by using the current REST API interface.
  • Maintained existing pagination, GraphQL behavior, query construction, and response handling.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: f608382e-2c84-4b4a-a7fb-53e61ce1eee8

📥 Commits

Reviewing files that changed from the base of the PR and between 3b2ef86 and 6c6221c.

📒 Files selected for processing (3)

• backend/__tests__/mocks/@octokit/core.js
• backend/lib/github/index.js
• backend/lib/github/octokit.js

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📝 Walkthrough

Walkthrough

The GitHub client now uses Octokit’s rest namespace for issue operations. The Octokit mock uses the same namespace and the restEndpointMethods plugin.

Changes

Octokit REST migration

Layer / File(s)	Summary
Configure Octokit REST methods backend/lib/github/octokit.js, backend/__tests__/mocks/@octokit/core.js	The client and mock use restEndpointMethods. Mocked issue methods are exposed under octokit.rest.issues.
Migrate GitHub issue calls backend/lib/github/index.js	Issue search, retrieval, updates, and comment creation use octokit.rest.issues.

Estimated code review effort: 1 (Trivial) | ~5 minutes

Possibly related PRs

• gardener/dashboard#3146: Upgrades the Octokit plugin dependency used by this migration.

Suggested reviewers: gardener-ci-robot

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description check	✅ Passed	The description uses the required template and provides categorization, purpose, issue status, reviewer notes, and release-note information.
Title check	✅ Passed	The title clearly and concisely describes the migration to Octokit’s REST namespace.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[grolu]

/hold
need to verify if this still works end-to-end

[petersutter]

/lgtm
/approve

[gardener-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: petersutter

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• OWNERS [petersutter]

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[gardener-prow]

LGTM label has been added.

Details

Git tree hash: ef4356682be3ea1fb24aba2dacd2e9fa6d9afca1

[petersutter]

need to verify if this still works end-to-end

fwiw I tested it and it seems to still work