Bump gatsby-remark-responsive-iframe from 2.4.12 to 6.13.1

Bumps [gatsby-remark-responsive-iframe](https://github.com/gatsbyjs/gatsby/tree/HEAD/packages/gatsby-remark-responsive-iframe) from 2.4.12 to 6.13.1.
- [Release notes](https://github.com/gatsbyjs/gatsby/releases)
- [Changelog](https://github.com/gatsbyjs/gatsby/blob/master/packages/gatsby-remark-responsive-iframe/CHANGELOG.md)
- [Commits](https://github.com/gatsbyjs/gatsby/commits/[email protected]/packages/gatsby-remark-responsive-iframe)

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

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