Bump decap-cms-app from 3.0.12 to 3.4.0

Bumps [decap-cms-app](https://github.com/decaporg/decap-cms) from 3.0.12 to 3.4.0.
- [Release notes](https://github.com/decaporg/decap-cms/releases)
- [Changelog](https://github.com/decaporg/decap-cms/blob/main/CHANGELOG.md)
- [Commits](https://github.com/decaporg/decap-cms/compare/[email protected]@3.4.0)

---
updated-dependencies:
- dependency-name: decap-cms-app
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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