build(deps): bump gatsby-plugin-sitemap from 5.4.0 to 5.6.0 in /docs (golangci#2542)

Bumps [gatsby-plugin-sitemap](https://github.com/gatsbyjs/gatsby/tree/HEAD/packages/gatsby-plugin-sitemap) from 5.4.0 to 5.6.0.
- [Release notes](https://github.com/gatsbyjs/gatsby/releases)
- [Changelog](https://github.com/gatsbyjs/gatsby/blob/master/packages/gatsby-plugin-sitemap/CHANGELOG.md)
- [Commits](https://github.com/gatsbyjs/gatsby/commits/[email protected]/packages/gatsby-plugin-sitemap)

---
updated-dependencies:
- dependency-name: gatsby-plugin-sitemap
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

docs/package-lock.json

@@ -25,7 +25,7 @@
     "gatsby-plugin-react-svg": "^3.1.0",
     "gatsby-plugin-robots-txt": "^1.6.14",
     "gatsby-plugin-sharp": "^3.10.2",
-    "gatsby-plugin-sitemap": "^5.4.0",
+    "gatsby-plugin-sitemap": "^5.6.0",
     "gatsby-remark-autolink-headers": "^2.11.0",
     "gatsby-remark-copy-linked-files": "^5.4.0",
     "gatsby-remark-embedder": "^4.2.0",