Bump ejs from 3.1.5 to 3.1.7 in /backend

Bumps [ejs](https://github.com/mde/ejs) from 3.1.5 to 3.1.7.
- [Release notes](https://github.com/mde/ejs/releases)
- [Changelog](https://github.com/mde/ejs/blob/main/CHANGELOG.md)
- [Commits](mde/ejs@v3.1.5...v3.1.7)

---
updated-dependencies:
- dependency-name: ejs
  dependency-type: direct:production
...

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Author: dependabot[bot]