Bump serve-static and express in /tools/st-prom-exporter

Bumps [serve-static](https://github.com/expressjs/serve-static) to 1.16.0 and updates ancestor dependency [express](https://github.com/expressjs/express). These dependencies need to be updated together.


Updates `serve-static` from 1.15.0 to 1.16.0
- [Release notes](https://github.com/expressjs/serve-static/releases)
- [Changelog](https://github.com/expressjs/serve-static/blob/master/HISTORY.md)
- [Commits](expressjs/serve-static@v1.15.0...1.16.0)

Updates `express` from 4.19.2 to 4.20.0
- [Release notes](https://github.com/expressjs/express/releases)
- [Changelog](https://github.com/expressjs/express/blob/master/History.md)
- [Commits](expressjs/express@4.19.2...4.20.0)

---
updated-dependencies:
- dependency-name: serve-static
  dependency-type: indirect
- dependency-name: express
  dependency-type: direct:production
...

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

tools/st-prom-exporter/package.json

@@ -12,7 +12,7 @@
   "license": "Unicode-3.0",
   "dependencies": {
     "bent": "^7.3.10",
-    "express": "^4.19.2",
+    "express": "^4.20.0",
     "prom-client": "^12.0.0"
   },
   "repository": {