Bump @mui/material from 5.15.7 to 5.15.9 (#962)

Bumps [@mui/material](https://github.com/mui/material-ui/tree/HEAD/packages/mui-material) from 5.15.7 to 5.15.9.
- [Release notes](https://github.com/mui/material-ui/releases)
- [Changelog](https://github.com/mui/material-ui/blob/master/CHANGELOG.md)
- [Commits](https://github.com/mui/material-ui/commits/v5.15.9/packages/mui-material)

---
updated-dependencies:
- dependency-name: "@mui/material"
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

package.json

@@ -12,7 +12,7 @@
  "@gatsbyjs/reach-router": "^2.0.1",
  "@mdx-js/react": "^2.3.0",
  "@mui/lab": "^5.0.0-alpha.164",
- "@mui/material": "^5.14.10",
+ "@mui/material": "^5.15.9",
  "@mui/x-data-grid": "^6.14.0",
  "@mui/x-date-pickers": "^6.19.3",
  "@popperjs/core": "^2.11.8",