fix: Mattb/upgrade cosign installer (#460)

* Upgrade cosign installer to v3.4.0

* upgrade cosign installer using same syntax as the indexer project

.github/workflows/docker-publish.yml

@@ -99,9 +99,7 @@ jobs:
       # transparency data even for private images, pass --force to cosign below.
       # https://github.com/sigstore/cosign
       - name: Install Cosign
-        uses: sigstore/cosign-installer@main
-        with:
-          cosign-release: 'v3.4.0'
+        uses: sigstore/[email protected]
       - name: Check install!
         run: cosign version
       - name: Sign the published Docker image