chore(deps-dev): bump sinon

Bumps the dev-sinon group in /packages/socket-mode with 1 update: [sinon](https://github.com/sinonjs/sinon).


Updates `sinon` from 20.0.0 to 21.0.0
- [Release notes](https://github.com/sinonjs/sinon/releases)
- [Changelog](https://github.com/sinonjs/sinon/blob/main/docs/changelog.md)
- [Commits](https://github.com/sinonjs/sinon/commits)

---
updated-dependencies:
- dependency-name: sinon
  dependency-version: 21.0.0
  dependency-type: direct:development
  update-type: version-update:semver-major
  dependency-group: dev-sinon
...

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

Author: dependabot[bot]

packages/socket-mode/package.json

@@ -68,7 +68,7 @@
     "nodemon": "^3.1.0",
     "proxyquire": "^2.1.3",
     "shx": "^0.4.0",
-    "sinon": "^20",
+    "sinon": "^21",
     "source-map-support": "^0.5.21",
     "ts-node": "^10",
     "typescript": "5.8.3"