Update gatsby monorepo

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
gatsby (changelog)	dependencies	patch	2.23.3 -> 2.23.4
gatsby-transformer-remark	dependencies	patch	2.8.15 -> 2.8.16

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Release Notes

gatsbyjs/gatsby

### [`v2.23.4`](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.23.3...gatsby@2.23.4) [Compare Source](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.23.3...gatsby@2.23.4)

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