Bump the VERSION variable in the Makefile and open a PR to update it. Make sure KO_VERSION is the latest version according to its github repo.
Once merged, create a tag with the same name as the new version, then create a release in the github UI. Once the release is created, run make image. This will use ko to create the new multiarch image and push it to $REGISTRY/gcp-auth-webhook according to the REGISTRY variable in the Makefile.