ci: add stale bot

[lumirlumir]

Prerequisites checklist

• I have read the contributing guidelines.

AI acknowledgment

• I did not use AI to generate this PR.
• (If the above is not checked) I have reviewed the AI-generated content before submitting.

What is the purpose of this pull request?

This PR simply adds a stale bot automation workflow, as decided in eslint/workflows#4 for the centralized workflow.

I’ve also updated the ci.yml workflow, as it behaved incorrectly in some cases.

What changes did you make? (Give an overview)

Added stale.yml workflow file.

Related Issues

Ref: eslint/workflows#4

Is there anything you'd like reviewers to focus on?

N/A

[Copilot]

Pull request overview

Adds automation to mark/close stale issues and PRs via ESLint’s centralized reusable workflow, and tweaks CI filtering logic for running tests on changed codemods.

Changes:

• Add a scheduled stale workflow that calls eslint/workflows’ reusable stale workflow.
• Update the CI “changed codemods” filter generation logic (currently introduces a sed runtime error).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
.github/workflows/stale.yml	Adds a scheduled workflow to run the centralized stale-bot reusable workflow.
.github/workflows/ci.yml	Modifies the shell pipeline that builds pnpm --filter arguments for changed codemods.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[lumirlumir]

This change handles PRs that do not touch codemod packages. Without this, grep '^codemods/' exits with 1 when there are no matching paths, causing the CI step to fail before it can skip tests.