NPM, Unity and HTTP status code 405

this is an issue I get when using GitHub’s NPM registry as Scoped Registry with Unity’s Package Manager (UPM). The issue might reside on Unity’s side, but since it only occurs with GitHub’s (and GitHub Enterprise’s) registries, I’m filing it here as well.

This is the error message printed by Unity:

[Package Manager Window] Cannot perform upm operation: Unable to perform online search:
  Request [GET] failed with status code [405] 

The UPM’s manifest.json has the scoped registry set up like this

  "scopedRegistries": [
      "name": "GitHub Packages (KageKirin)",
      "url": "",
      "scopes": [
  "dependencies": {
    "com.kagekirin.createurpshaders": "1.0.6",

So far, this setup works to fetch my package from the registry where I published it,
but it would be lovely not to get the spam about failed searches.

Thanks for any help.