fix(kms): revert hardhat to v2 for peer dependency compatibility

hardhat v3 is incompatible with @nomicfoundation/hardhat-ethers@3.x
and @openzeppelin/hardhat-upgrades@3.x which require hardhat ^2.0.0.

Author: kvinwang

kms/auth-eth/package.json

@@ -23,12 +23,12 @@
   },
   "devDependencies": {
     "@nomicfoundation/hardhat-ethers": "^3.0.8",
-    "@nomicfoundation/hardhat-toolbox": "^7.0.0",
+    "@nomicfoundation/hardhat-toolbox": "^4.0.0",
     "@openzeppelin/hardhat-upgrades": "^3.9.0",
     "@types/jest": "^29.5.14",
     "@types/node": "^20.17.12",
     "@types/supertest": "^6.0.2",
-    "hardhat": "^3.1.11",
+    "hardhat": "^2.22.17",
     "jest": "^29.7.0",
     "supertest": "^6.3.3",
     "ts-jest": "^29.1.1",