chore(deps): update dependency mocha to v9 (#174)

Co-authored-by: Maggie Nolan <nolanmar@google.com>

Author: renovate-bot

package-lock.json

@@ -41,7 +41,7 @@
     "split": "^1.0.1"
   },
   "devDependencies": {
-    "@types/mocha": "^8.0.0",
+    "@types/mocha": "^9.0.0",
     "@types/node": "^15.6.1",
     "@types/p-limit": "^2.0.0",
     "@types/pify": "^5.0.0",
@@ -54,7 +54,7 @@
     "gts": "^3.0.0",
     "js-green-licenses": "^3.0.0",
     "linkinator": "^2.0.0",
-    "mocha": "^8.0.0",
+    "mocha": "^9.0.0",
     "nyc": "^15.0.0",
     "sinon": "^11.1.0",
     "source-map-support": "^0.5.12",