deps: "downgrade" node-fetch to ^v2.6.7 in script/

This version has all the known security patches in v3.x,
and is meanwhile the recommended version to use from CommonJS
(NodeJS-style) modules, as opposed to ESM.

Atom's build and CI scripts are all CommonJS as far as I know,
so we should basically stay on node-fetch v2.x.

This fixes the currently broken "Bump dependencies" job in Nightly CI.

Effectively reverts ad1318e,
AKA atom#23506,
albeit with a more up-to-date patch version of node-fetch v2.x.

Author: DeeDeeG

script/package-lock.json

@@ -35,7 +35,7 @@
     "minidump": "^0.22.0",
     "mkdirp": "0.5.1",
     "nock": "^13.0.2",
-    "node-fetch": "^3.1.1",
+    "node-fetch": "^2.6.7",
     "normalize-package-data": "2.3.5",
     "npm": "^6.14.16",
     "npm-check": "^5.9.2",