build(deps): bump gatsby-transformer-remark in /gatsby-theme-mate

Bumps [gatsby-transformer-remark](https://github.com/gatsbyjs/gatsby/tree/HEAD/packages/gatsby-transformer-remark) from 5.25.1 to 6.12.3.
- [Release notes](https://github.com/gatsbyjs/gatsby/releases)
- [Changelog](https://github.com/gatsbyjs/gatsby/blob/master/packages/gatsby-transformer-remark/CHANGELOG.md)
- [Commits](https://github.com/gatsbyjs/gatsby/commits/gatsby-transformer-remark@6.12.3/packages/gatsby-transformer-remark)

---
updated-dependencies:
- dependency-name: gatsby-transformer-remark
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

gatsby-theme-mate/package.json

@@ -41,7 +41,7 @@
     "gatsby-plugin-typescript": "^4.10.0",
     "gatsby-source-contentful": "^7.8.1",
     "gatsby-source-medium": "^4.10.0",
-    "gatsby-transformer-remark": "^5.10.1",
+    "gatsby-transformer-remark": "^6.12.3",
     "gatsby-plugin-fontawesome-css": "^1.2.0",
     "react-awesome-reveal": "^3.8.1",
     "react-headroom": "^3.2.0",