fix: add cosign registry login for Helm chart signing

The cosign sign step needs its own authentication to ghcr.io to push
signature blobs. The existing helm registry login does not share
credentials with cosign.

Signed-off-by: Simon Lauger <simon@lauger.de>

Author: slauger

.github/workflows/release.yaml

@@ -113,7 +113,9 @@ jobs:
         uses: sigstore/cosign-installer@v4.1.2
 
       - name: Login to ghcr.io
-        run: echo "${{ github.token }}" | helm registry login ghcr.io -u ${{ github.actor }} --password-stdin
+        run: |
+          echo "${{ github.token }}" | helm registry login ghcr.io -u ${{ github.actor }} --password-stdin
+          echo "${{ github.token }}" | cosign login ghcr.io -u ${{ github.actor }} --password-stdin
 
       - name: Inject version into Chart.yaml
         run: |