Bump gatsby from 3.15.0 to 5.15.0

Bumps [gatsby](https://github.com/gatsbyjs/gatsby) from 3.15.0 to 5.15.0.
- [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]@5.15.0)

---
updated-dependencies:
- dependency-name: gatsby
  dependency-version: 5.15.0
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

docs/package.json

@@ -12,7 +12,7 @@
   "dependencies": {
     "@primer/gatsby-theme-doctocat": "*",
     "@primer/react": "^36.1.0",
-    "gatsby": "^3.14.0",
+    "gatsby": "^5.15.0",
     "react": "^18.2.0",
     "react-dom": "^18.2.0"
   },