Bump @astrojs/rss from 4.0.12 to 4.0.13

Bumps [@astrojs/rss](https://github.com/withastro/astro/tree/HEAD/packages/astro-rss) from 4.0.12 to 4.0.13.
- [Release notes](https://github.com/withastro/astro/releases)
- [Changelog](https://github.com/withastro/astro/blob/main/packages/astro-rss/CHANGELOG.md)
- [Commits](https://github.com/withastro/astro/commits/@astrojs/rss@4.0.13/packages/astro-rss)

---
updated-dependencies:
- dependency-name: "@astrojs/rss"
  dependency-version: 4.0.13
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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Author: dependabot[bot]