Bump sigstore/cosign-installer from 3.8.1 to 3.9.1 (#20)

---
updated-dependencies:
- dependency-name: sigstore/cosign-installer
  dependency-version: 3.9.1
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.github/workflows/docker-publish.yml

@@ -39,7 +39,7 @@ jobs:
       # https://github.com/sigstore/cosign-installer
       - name: Install cosign
         if: github.event_name != 'pull_request'
-        uses: sigstore/cosign-installer@d7d6bc7722e3daa8354c50bcb52f4837da5e9b6a #v3.8.1
+        uses: sigstore/cosign-installer@398d4b0eeef1380460a10c8013a76f728fb906ac #v3.9.1
         with:
           cosign-release: 'v2.2.4'