fix: unblock release by upgrading @types/sinon for the add optimize package (#8258)

## Description

Although the release https://togithub.com/googleapis/google-cloud-node/pull/8254 is merged, it is failing to publish because the google-cloud-optimize package is failing to compile. This is confirmed by checking out main and running the following commands which produce a compile time error:

```
cd packages/google-cloud-appoptimize/
npm cache clean --force
rm -rf node_modules package-lock.json
npm install
```

The error goes away when installing the latest version of `@types/sinon`. A similar issue was solved in https://togithub.com/googleapis/google-cloud-node/pull/8098.

## Impact

Allows us to publish releases again for google-cloud-node.

Author: danieljbruce

packages/google-cloud-appoptimize/package.json

@@ -50,7 +50,7 @@
   "devDependencies": {
     "@types/mocha": "^10.0.10",
     "@types/node": "^22.13.9",
-    "@types/sinon": "^17.0.4",
+    "@types/sinon": "^21.0.1",
     "c8": "^10.1.3",
     "gapic-tools": "^1.0.0",
     "gts": "^6.0.2",