Chore(deps): Bump express from 4.19.2 to 4.21.0

Bumps [express](https://github.com/expressjs/express) from 4.19.2 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@4.19.2...4.21.0)

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

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

package.json

@@ -33,7 +33,7 @@
  "eslint-config-react-app": "7.0.1",
  "eslint-plugin-react": "7.33.2",
  "eslint-webpack-plugin": "4.1.0",
- "express": "4.19.2",
+ "express": "4.21.0",
  "expvariantassignmentsdk": "file:packages/expvariantassignmentsdk-1.0.0.tgz",
  "file-loader": "6.2.0",
  "fork-ts-checker-webpack-plugin": "9.0.2",