Bump path-to-regexp and express in /backend

Bumps [path-to-regexp](https://github.com/pillarjs/path-to-regexp) to 0.1.10 and updates ancestor dependency [express](https://github.com/expressjs/express). These dependencies need to be updated together.


Updates `path-to-regexp` from 0.1.7 to 0.1.10
- [Release notes](https://github.com/pillarjs/path-to-regexp/releases)
- [Changelog](https://github.com/pillarjs/path-to-regexp/blob/master/History.md)
- [Commits](pillarjs/path-to-regexp@v0.1.7...v0.1.10)

Updates `express` from 4.17.1 to 4.21.0
- [Release notes](https://github.com/expressjs/express/releases)
- [Changelog](https://github.com/expressjs/express/blob/4.21.0/History.md)
- [Commits](expressjs/express@4.17.1...4.21.0)

---
updated-dependencies:
- dependency-name: path-to-regexp
  dependency-type: indirect
- dependency-name: express
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>