Bump path-to-regexp and express in /react-express-mongodb/backend

Bumps [path-to-regexp](https://github.com/pillarjs/path-to-regexp) to 0.1.12 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 0.1.12
- [Release notes](https://github.com/pillarjs/path-to-regexp/releases)
- [Changelog](https://github.com/pillarjs/path-to-regexp/blob/master/History.md)
- [Commits](https://github.com/pillarjs/path-to-regexp/compare/v0.1.7...v0.1.12)

Updates `express` from 4.17.1 to 4.21.2
- [Release notes](https://github.com/expressjs/express/releases)
- [Changelog](https://github.com/expressjs/express/blob/4.21.2/History.md)
- [Commits](https://github.com/expressjs/express/compare/4.17.1...4.21.2)

---
updated-dependencies:
- dependency-name: path-to-regexp
  dependency-version: 0.1.12
  dependency-type: indirect
- dependency-name: express
  dependency-version: 4.21.2
  dependency-type: direct:production
...

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

react-express-mongodb/backend/package.json

@@ -16,7 +16,7 @@
     "body-parser": "^1.18.2",
     "cookie-parser": "^1.4.4",
     "cors": "^2.8.4",
-    "express": "^4.17.1",
+    "express": "^4.21.2",
     "lodash": "^4.17.13",
     "mongodb": "^3.0.7",
     "mongoose": "^6.0.9",