The release script fails to publish proper checksums and their signatures

[cardil]

As evidenced by kn-event 1.9.1 release job, the release script fails to publish a proper checksum file, together with (.sig and .pem) files.

The files at gs bucket are valid, but the checksums.txt file published at Github releases was invalid.

I suspect the stale checksums.txt (before MacOS signing) was published on Github releases, and that caused the upload command to fail.

/kind bug

[cardil]

I've downloaded all the artifacts from the Github to compare them with gs bucket. It looks like all binaries are not matching the ones from the bucket:

---

The above is false. I mistakenly downloaded the nightly bucket instead of release. 🤦‍♂️

[cardil]

The changes done in #268 are not enough to make an errorless release. Further work needs to be done.

Follow up from #240

[cardil]

For whatever reason, the script doesn't find the checksums.txt file produced by kn-event build:

https://prow.knative.dev/view/gs/knative-prow/logs/release_kn-plugin-event_release-1.9_periodic/1625125552232861696#1:build-log.txt%3A1301

As a result, the $ARTIFACTS_TO_PUBLISH variable contains two checksums.txt files, and that breaks the artifact to upload to the GitHub page (GH API responds the name of the artifact is duplicated).