chore(deps): bump @slack/bolt in /examples/custom-receiver

Bumps [@slack/bolt](https://github.com/slackapi/bolt-js) from 3.22.0 to 4.2.0.
- [Release notes](https://github.com/slackapi/bolt-js/releases)
- [Commits](https://github.com/slackapi/bolt-js/compare/@slack/bolt@3.22.0...@slack/bolt@4.2.0)

---
updated-dependencies:
- dependency-name: "@slack/bolt"
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

examples/custom-receiver/package.json

@@ -12,7 +12,7 @@
   "license": "MIT",
   "dependencies": {
     "@koa/router": "^13",
-    "@slack/bolt": "^3",
+    "@slack/bolt": "^4",
     "@slack/logger": "^4.0.0",
     "@slack/oauth": "^3",
     "dotenv": "^16",