fix(ci): grant contents:write for SBOM release asset upload

anchore/sbom-action attaches SBOMs to GitHub releases, which requires
write access to contents. The workflow previously only had read access,
causing 'Resource not accessible by integration' errors.

.github/workflows/docker-publish.yml

@@ -12,7 +12,7 @@ jobs:
     runs-on: ubuntu-latest
     timeout-minutes: 30
     permissions:
-      contents: read
+      contents: write
       packages: write
       id-token: write
       attestations: write