ci: fix a really small typo expecting tags to start with v (#393)

Author: alecbcs

.github/workflows/container.yml

@@ -62,7 +62,7 @@ jobs:
           cache-from: type=registry,ref=ghcr.io/spack/tutorial:buildcache
           cache-to: ${{ github.ref == github.event.repository.default_branch
                       && 'type=registry,ref=ghcr.io/spack/tutorial:buildcache,mode=max' || '' }}
-          outputs: ${{ (github.ref == github.event.repository.default_branch || startsWith(github.ref, 'refs/tags/v'))
+          outputs: ${{ (github.ref == github.event.repository.default_branch || startsWith(github.ref, 'refs/tags/'))
                       && 'type=registry' || 'type=docker,dest=/tmp/tutorial-container.tar' }}
 
       - name: Upload container as artifact for PRs