deps: bump ethers from 6.14.4 to 6.15.0

Bumps [ethers](https://github.com/ethers-io/ethers.js) from 6.14.4 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@v6.14.4...v6.15.0)

---
updated-dependencies:
- dependency-name: ethers
  dependency-version: 6.15.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

observer/package.json

@@ -21,7 +21,7 @@
     "@sentry/node": "^9.32.0",
     "@types/slug": "^5.0.9",
     "debug": "^4.4.1",
-    "ethers": "^6.14.4",
+    "ethers": "^6.15.0",
     "pg": "^8.16.0",
     "slug": "^11.0.0"
   },