build(deps): update whatwg-fetch requirement

Updates the requirements on [whatwg-fetch](https://github.com/github/fetch) to permit the latest version.
- [Release notes](https://github.com/github/fetch/releases)
- [Changelog](https://github.com/JakeChampion/fetch/blob/main/CHANGELOG.md)
- [Commits](JakeChampion/fetch@v3.0.0...v3.6.20)

---
updated-dependencies:
- dependency-name: whatwg-fetch
  dependency-type: direct:production
...

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

superset-frontend/packages/superset-ui-core/package.json

@@ -60,7 +60,7 @@
     "reselect": "^4.0.0",
     "rison": "^0.1.1",
     "seedrandom": "^3.0.5",
-    "whatwg-fetch": "^3.0.0",
+    "whatwg-fetch": "^3.6.20",
     "xss": "^1.0.14"
   },
   "devDependencies": {