Bump gatsby from 5.14.6 to 5.15.0 in /website (#322)

Bumps [gatsby](https://github.com/gatsbyjs/gatsby) from 5.14.6 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/gatsby@5.14.6...gatsby@5.15.0)

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

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

Author: dependabot[bot]

website/package.json

@@ -22,7 +22,7 @@
     "@fortawesome/free-solid-svg-icons": "^7.0.0",
     "@fortawesome/react-fontawesome": "^3.1.0",
     "bulma": "^1.0.4",
-    "gatsby": "^5.14.6",
+    "gatsby": "^5.15.0",
     "gatsby-plugin-image": "^3.15.0",
     "gatsby-plugin-manifest": "^5.14.0",
     "gatsby-plugin-react-helmet": "^6.15.0",