chore(deps): avoid packages/testing local deps out of sync (#6190)

See #6188.

The `packages/testing` package has dev dependencies on `packages/build` and
`packages/config`, but these also have (undeclared) dev dependencies on
`packages/testing`.

Since our release-please configuration does not include `packages/testing` at all (there's
nothing to release; it's a "local package" only), major bumps to either of its
dependencies results in `packages/testing` no longer pulling in their local versions and
instead pulls in a duplicated previous published version from the NPM registry.

This in turn results in `@netlify/config` and/or `@netlify/build` not actually testing
their own source, since they use `packages/testing` to test themselves...

This is a confusing mess, and [declaring the missing dependencies does not
work](#6133) because `nx` detects the circular
dependency and aborts 😭.

This prevents the problem from reoccuring.

Author: serhalp

package-lock.json

@@ -16,8 +16,8 @@
     "build": "tsc"
   },
   "devDependencies": {
-    "@netlify/build": "^31.0.0",
-    "@netlify/config": "^21.0.7",
+    "@netlify/build": "*",
+    "@netlify/config": "*",
     "@types/lodash-es": "^4.17.6",
     "@types/node": "^14.18.53",
     "ava": "^4.0.0",