Bump ethers from 5.7.2 to 6.8.0 in /packages/proposal

Bumps [ethers](https://github.com/ethers-io/ethers.js) from 5.7.2 to 6.8.0.
- [Release notes](https://github.com/ethers-io/ethers.js/releases)
- [Changelog](https://github.com/ethers-io/ethers.js/blob/main/CHANGELOG.md)
- [Commits](ethers-io/ethers.js@v5.7.2...v6.8.0)

---
updated-dependencies:
- dependency-name: ethers
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

packages/proposal/package.json

@@ -22,7 +22,7 @@
   "dependencies": {
     "@openzeppelin/defender-sdk-base-client": "^1.3.0",
     "axios": "^1.4.0",
-    "ethers": "^5.7.2",
+    "ethers": "^6.8.0",
     "lodash": "^4.17.21"
   },
   "publishConfig": {