chore(deps): bump gatsby-theme-blog-core from 1.0.70 to 1.2.29

Bumps [gatsby-theme-blog-core](https://github.com/gatsbyjs/gatsby/tree/HEAD/packages/gatsby-theme-blog-core) from 1.0.70 to 1.2.29.
- [Release notes](https://github.com/gatsbyjs/gatsby/releases)
- [Changelog](https://github.com/gatsbyjs/gatsby/blob/master/packages/gatsby-theme-blog-core/CHANGELOG.md)
- [Commits](https://github.com/gatsbyjs/gatsby/commits/[email protected]/packages/gatsby-theme-blog-core)

Signed-off-by: dependabot-preview[bot] <[email protected]>

Author: dependabot-preview[bot]