chore(docs): update doctocat theme

[joshblack]

Note: this PR depends on: https://github.com/primer/doctocat/pull/479

This PR update gatsby to use a prerelease version of the doctocat theme which has also been updated to support v3.

Checklist

• [x] Update Gatsby to 3.x
• [x] Update Gatsby-related packages
• [x] Update @primer/gatsby-theme-doctocat

[changeset-bot[bot]]

⚠️ No Changeset found

Latest commit: 30516ae71abbea892304b39e175c9c5c3afa9ac7

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

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[github-actions[bot]]

size-limit report 📦

Path	Size
dist/browser.esm.js	76.3 KB (0%)
dist/browser.umd.js	76.94 KB (0%)

[github-actions[bot]]

size-limit report 📦

Path	Size
dist/browser.esm.js	76.3 KB (0%)
dist/browser.umd.js	76.94 KB (0%)