build(deps): bump gatsby-plugin-manifest from 2.4.21 to 2.4.23 in /docs (#1309)

Bumps [gatsby-plugin-manifest](https://github.com/gatsbyjs/gatsby/tree/HEAD/packages/gatsby-plugin-manifest) from 2.4.21 to 2.4.23.
- [Release notes](https://github.com/gatsbyjs/gatsby/releases)
- [Changelog](https://github.com/gatsbyjs/gatsby/blob/master/packages/gatsby-plugin-manifest/CHANGELOG.md)
- [Commits](https://github.com/gatsbyjs/gatsby/commits/gatsby-plugin-manifest@2.4.23/packages/gatsby-plugin-manifest)

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

Author: dependabot[bot]

docs/package-lock.json

@@ -17,7 +17,7 @@
     "gatsby-plugin-catch-links": "^2.3.11",
     "gatsby-plugin-emotion": "^4.3.10",
     "gatsby-plugin-google-analytics": "^2.3.13",
-    "gatsby-plugin-manifest": "^2.4.21",
+    "gatsby-plugin-manifest": "^2.4.23",
     "gatsby-plugin-mdx": "^1.2.30",
     "gatsby-plugin-netlify": "^2.3.12",
     "gatsby-plugin-netlify-cache": "^1.2.0",