build(deps-dev): bump ember-cli-showdown from 6.0.1 to 7.0.0

Bumps [ember-cli-showdown](https://github.com/empress/ember-cli-showdown) from 6.0.1 to 7.0.0.
- [Release notes](https://github.com/empress/ember-cli-showdown/releases)
- [Changelog](https://github.com/empress/ember-cli-showdown/blob/main/CHANGELOG.md)
- [Commits](empress/ember-cli-showdown@v6.0.1...v7.0.0)

---
updated-dependencies:
- dependency-name: ember-cli-showdown
  dependency-type: direct:development
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]