Update @types/koa requirement from ^2.11.4 to ^2.13.4

Updates the requirements on [@types/koa](https://github.com/DefinitelyTyped/DefinitelyTyped/tree/HEAD/types/koa) to permit the latest version.
- [Release notes](https://github.com/DefinitelyTyped/DefinitelyTyped/releases)
- [Commits](https://github.com/DefinitelyTyped/DefinitelyTyped/commits/HEAD/types/koa)

---
updated-dependencies:
- dependency-name: "@types/koa"
  dependency-type: direct:development
...

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

package.json

@@ -49,7 +49,7 @@
   "devDependencies": {
     "@google-cloud/datastore": "^6.3.1",
     "@types/fs-extra": "^9.0.7",
-    "@types/koa": "^2.11.6",
+    "@types/koa": "^2.13.4",
     "@types/koa-bodyparser": "^4.3.0",
     "@types/koa-compress": "^4.0.1",
     "@types/koa-logger": "^3.1.1",