set cosign-installer to use default (latest) cosign version (#242)

Author: aobort

.github/workflows/docker-publish.yaml

@@ -36,8 +36,6 @@ jobs:
       - name: Install cosign
         if: github.event_name != 'pull_request'
         uses: sigstore/[email protected]
-        with:
-          cosign-release: 'v2.1.1'
 
       # Set up BuildKit Docker container builder to be able to build
       # multi-platform images and export cache