Bump gatsby from 4.25.7 to 5.12.9

Bumps [gatsby](https://github.com/gatsbyjs/gatsby) from 4.25.7 to 5.12.9.
- [Release notes](https://github.com/gatsbyjs/gatsby/releases)
- [Changelog](https://github.com/gatsbyjs/gatsby/blob/master/CHANGELOG.md)
- [Commits](https://github.com/gatsbyjs/gatsby/compare/[email protected]@5.12.9)

---
updated-dependencies:
- dependency-name: gatsby
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

packages/gatsby-mdx/package.json

@@ -8,7 +8,7 @@
 		"@mdx-js/react": "^1.0.6",
 		"@mdx-js/tag": "^0.20.3",
 		"babel-plugin-styled-components": "^1.10.0",
-		"gatsby": "^2.3.24",
+		"gatsby": "^5.12.9",
 		"gatsby-image": "^2.0.39",
 		"gatsby-mdx": "^0.6.2",
 		"gatsby-plugin-manifest": "^2.0.29",