chore(deps): update dependency @types/mocha to v9 (#7)

Author: renovate-bot

packages/google-cloud-video-stitcher/package.json

@@ -42,7 +42,7 @@
     "google-gax": "^3.0.0"
   },
   "devDependencies": {
-    "@types/mocha": "^8.2.2",
+    "@types/mocha": "^9.0.0",
     "@types/node": "^14.14.44",
     "@types/sinon": "^10.0.0",
     "c8": "^7.7.2",