add actions write permission to stale workflow

[Thenlie]

What does this PR do?

Improve repo

For resources

Description

This PR attempts to resolve the above error.

When the action attempts to update the actions cache, it fails. Based on actions/stale#1131, it seems that issue may be permission related.

I will also be manually deleting the cache to ensure all PRs are processed.

Why is this valuable (or not)?

How do we know it's really free?

For book lists, is it a book? For course lists, is it a course? etc.

Checklist:

• Read our contributing guidelines.
• Search for duplicates.
• Include author(s) and platform where appropriate.
• Put lists in alphabetical order, correct spacing.
• Add needed indications (PDF, access notes, under construction).
• Used an informative name for this pull request.

Follow-up

• Check the status of GitHub Actions and resolve any reported warnings!