Update dependency gatsby to v2.21.9

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
gatsby (changelog)	dependencies	patch	2.21.7 -> 2.21.9

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Release Notes

gatsbyjs/gatsby

### [`v2.21.9`](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.21.8...gatsby@2.21.9) [Compare Source](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.21.8...gatsby@2.21.9) ### [`v2.21.8`](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.21.7...gatsby@2.21.8) [Compare Source](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.21.7...gatsby@2.21.8)

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