Bump shell-quote and gatsby

Bumps [shell-quote](https://github.com/substack/node-shell-quote) and [gatsby](https://github.com/gatsbyjs/gatsby). These dependencies needed to be updated together.

Updates `shell-quote` from 1.7.2 to 1.7.3
- [Release notes](https://github.com/substack/node-shell-quote/releases)
- [Changelog](https://github.com/substack/node-shell-quote/blob/master/CHANGELOG.md)
- [Commits](https://github.com/substack/node-shell-quote/compare/v1.7.2...1.7.3)

Updates `gatsby` from 3.14.5 to 4.21.1
- [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/gatsby@3.14.5...gatsby@4.21.1)

---
updated-dependencies:
- dependency-name: shell-quote
  dependency-type: indirect
- dependency-name: gatsby
  dependency-type: direct:production
...

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Author: dependabot[bot]