ci: permit stale workflow to delete cache (#21772)

## Which issue does this PR close?

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N/A

## Rationale for this change

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Some PRs are being omitted from stale check because they were in a
cache, and the workflow appears to not have permission to delete cache
so they are forever stuck as unprocessed.

For example in this run:
https://github.com/apache/datafusion/actions/runs/24756695077/job/72431314533

Seeing this in logs:

```
[#20473]            issue skipped due being processed during the previous run
[#20460]            pull request skipped due being processed during the previous run
[#20448]            issue skipped due being processed during the previous run
[#20443]            issue skipped due being processed during the previous run
[#20435]            issue skipped due being processed during the previous run
[#20418]            issue skipped due being processed during the previous run
[#20417]            pull request skipped due being processed during the previous run
[#20416]            pull request skipped due being processed during the previous run
[#20403]            pull request skipped due being processed during the previous run
```

And at the end we see this warning:

```
Warning: Error delete _state: [403] Resource not accessible by integration - https://docs.github.com/rest/actions/cache#delete-github-actions-caches-for-a-repository-using-a-cache-key
```

stale workflow uses a cache in case it hits the `operations-per-run`
limit meant to prevent API rate limiting (we have default of 30), so it
seems we previously hit this limit and some issues/PRs were cached, and
have never been uncached since so are never processed again. See:
https://github.com/actions/stale#operations-per-run

## What changes are included in this PR?

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PR.
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Give permission to stale workflow to run github actions (like delete
cache). See recommended permissions:

https://github.com/actions/stale#recommended-permissions

## Are these changes tested?

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## Are there any user-facing changes?

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Author: Jefffrey

.github/workflows/stale.yml

@@ -24,6 +24,7 @@ jobs:
   close-stale-prs:
     runs-on: ubuntu-slim
     permissions:
+      actions: write
       issues: write
       pull-requests: write
     steps: