Bump sigstore/cosign-installer from 2.6.0 to 2.8.0

Bumps [sigstore/cosign-installer](https://github.com/sigstore/cosign-installer) from 2.6.0 to 2.8.0.
- [Release notes](https://github.com/sigstore/cosign-installer/releases)
- [Commits](f3c664df7a...7cc35d7fdb)

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

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/docker-publish.yml

@@ -41,7 +41,7 @@ jobs:
       # https://github.com/sigstore/cosign-installer
       - name: Install cosign
         if: github.event_name != 'pull_request'
-        uses: sigstore/cosign-installer@f3c664df7af409cb4873aa5068053ba9d61a57b6 #v2.6.0
+        uses: sigstore/cosign-installer@7cc35d7fdbe70d4278a0c96779081e6fac665f88 #v2.6.0
         with:
           cosign-release: 'v1.11.0'