build(deps-dev): bump ethers in /packages/network-contracts

Bumps [ethers](https://github.com/ethers-io/ethers.js) from 5.7.0 to 6.15.0.
- [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@v5.7.0...v6.15.0)

---
updated-dependencies:
- dependency-name: ethers
  dependency-version: 6.15.0
  dependency-type: direct:development
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

packages/network-contracts/package.json

@@ -71,7 +71,7 @@
     "@uniswap/v2-core": "^1.0.1",
     "@uniswap/v2-periphery": "^1.1.0-beta.0",
     "debug": "4.3.3",
-    "ethers": "5.7.0",
+    "ethers": "6.15.0",
     "hardhat": "2.13.1",
     "hardhat-contract-sizer": "2.10.0",
     "hardhat-dependency-compiler": "1.1.3",