Bump the npm_and_yarn group across 2 directories with 1 update

Bumps the npm_and_yarn group with 1 update in the /presentations/eissing-h2 directory: [express](https://github.com/expressjs/express).
Bumps the npm_and_yarn group with 1 update in the /presentations/reschke-headers directory: [express](https://github.com/expressjs/express).


Updates `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)

Updates `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
  dependency-group: npm_and_yarn
- dependency-name: express
  dependency-type: direct:production
  dependency-group: npm_and_yarn
...

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

Author: dependabot[bot]

presentations/eissing-h2/package.json

@@ -23,7 +23,7 @@
   },
   "dependencies": {
     "underscore": "~1.13.6",
-    "express": "~4.19.2",
+    "express": "~4.21.0",
     "mustache": "~4.2.0",
     "socket.io": "~4.7.3"
   },

presentations/reschke-headers/package.json

@@ -23,7 +23,7 @@
   },
   "dependencies": {
     "underscore": "~1.13.6",
-    "express": "~4.19.2",
+    "express": "~4.21.0",
     "mustache": "~4.2.0",
     "socket.io": "~4.7.3"
   },