build: Revert container image & explicitly install helm binary

.gitea/workflows/actions.yaml

@@ -100,12 +100,16 @@ jobs:
     name: Helm chart
     runs-on: dind
     needs: semrel_dryrun
-    container: code.spamasaurus.com/djpbessems/packer-extended:1.3.0
     steps:
       - name: Check out repository code
         uses: actions/checkout@v4
       - name: Prepare build environment
         run: |
+          curl -L https://api.github.com/repos/helm/helm/releases/latest | \
+            jq -r '.tag_name' | \
+            xargs -I {} curl -L -o /tmp/helm.tar.gz https://get.helm.sh/helm-{}-linux-amd64.tar.gz && \
+          tar -xzf /tmp/helm.tar.gz --strip-components=1 -C /bin
+
           helm plugin install https://github.com/chartmuseum/helm-push
 
           sed -i 's/{{ chart_version }}/${{ needs.semrel_dryrun.outputs.version }}/g' charts/json-server/Chart.yaml