chore(deps): bump gatsby from 5.6.0 to 5.8.1

Bumps [gatsby](https://github.com/gatsbyjs/gatsby) from 5.6.0 to 5.8.1.
- [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]@5.8.1)

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

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

packages/defaults/package.json

@@ -10,7 +10,7 @@
   },
   "dependencies": {
     "@thepolicylab-projectportals/gatsby-theme-project-portal": "0.0.0",
-    "gatsby": "^5.6.0",
+    "gatsby": "^5.8.1",
     "react": "^18.2.0",
     "react-dom": "^18.2.0"
   }

packages/example-site/package.json

@@ -11,7 +11,7 @@
   "dependencies": {
     "@thepolicylab-projectportals/gatsby-theme-project-portal": "0.0.0",
     "@thepolicylab-projectportals/project-portal-content-netlify": "0.0.0",
-    "gatsby": "^5.6.0",
+    "gatsby": "^5.8.1",
     "gatsby-plugin-sitemap": "^6.6.0",
     "react": "^18.2.0",
     "react-dom": "^18.2.0"

packages/example/package.json

@@ -10,7 +10,7 @@
   },
   "dependencies": {
     "@thepolicylab-projectportals/gatsby-theme-project-portal": "^0.0.0",
-    "gatsby": "^5.6.0",
+    "gatsby": "^5.8.1",
     "gatsby-plugin-image": "^3.6.0",
     "gatsby-plugin-sharp": "^5.6.0",
     "gatsby-source-filesystem": "^5.7.0",