Work around regression in sinonjs/fake-timers

Author: MarkDuckworth

handwritten/firestore/package.json

@@ -90,7 +90,7 @@
     "@types/extend": "^3.0.4",
     "@types/mocha": "^10.0.10",
     "@types/node": "^24.1.0",
-    "@types/sinon": "^17.0.4",
+    "@types/sinon": "^21.0.0",
     "@types/through2": "^2.0.41",
     "c8": "^10.1.3",
     "chai": "^4.5.0",
@@ -120,6 +120,13 @@
     "ts-node": "^10.9.2",
     "typescript": "^5.9.2"
   },
+  "//_comment": "TODO: Remove @sinonjs/fake-timers overrides/resolutions when version > 15.3.0 fixes the duplicate identifier 'withGlobal' issue.",
+  "overrides": {
+    "@sinonjs/fake-timers": "15.1.1"
+  },
+  "resolutions": {
+    "@sinonjs/fake-timers": "15.1.1"
+  },
   "exports": {
     ".": {
       "types": "./types/firestore.d.ts",