Bump sigstore/cosign-installer in the dependencies group (#9034)

Bumps the dependencies group with 1 update: [sigstore/cosign-installer](https://github.com/sigstore/cosign-installer).


Updates `sigstore/cosign-installer` from 3.7.0 to 3.8.0
- [Release notes](https://github.com/sigstore/cosign-installer/releases)
- [Commits](sigstore/cosign-installer@dc72c7d...c56c2d3)

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

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

.github/workflows/docker.yaml

@@ -136,7 +136,7 @@ jobs:
         uses: docker/setup-buildx-action@6524bf65af31da8d45b59e8c27de4bd072b392f5 # [email protected]
       - name: Set up cosign
         if: github.event_name != 'pull_request'
-        uses: sigstore/cosign-installer@dc72c7d5c4d10cd6bcb8cf6e3fd625a9e5e537da # pin@v3.7.0
+        uses: sigstore/cosign-installer@c56c2d3e59e4281cc41dea2217323ba5694b171e # pin@v3.8.0
       - name: Check if Dockerhub login is required
         id: docker_login
         run: |