build: fix path-to-regexp to older version due to node 14 requirement (…

…#1403)

Sinon depends on the [`nise` package](https://www.npmjs.com/package/nise). That package just published `v6.0.1` which updated `path-to-regexp` from `v6.2.1` to `v8.1.0` with https://togithub.com/sinonjs/nise/pull/226. That should have been a major version bump, as this ended up introducing a breaking change that now it depends on `Node >= 16`, which is causing our CI to break. 

This PR fixes `path-to-regexp` to `^6.2.1` like previously to make it work on `Node >= 14`

Similar to https://togithub.com/googleapis/nodejs-bigquery-storage/pull/475

package.json

@@ -84,6 +84,8 @@
     "prettier": "^3.0.0",
     "proxyquire": "^2.1.0",
     "sinon": "^18.0.0",
+    "nise": "6.0.0",
+    "path-to-regexp": "6.2.2",
     "typescript": "^5.1.6"
   }
 }