ci: fix publishing of ci-builder (#3004)

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

.changeset/itchy-carpets-fail.md

+---
+'@eth-optimism/ci-builder': patch
+---
+
+Fix publishing

.github/workflows/release.yml

@@ -232,8 +232,8 @@ jobs:
       - name: Publish ci-builder
         uses: docker/build-push-action@v2
         with:
-          context: .
-          file: ./ops/docker/ci-builder/Dockerfile
+          context: ./ops/docker/ci-builder
+          file: Dockerfile
           push: true
           tags: ethereumoptimism/ci-builder:${{ needs.release.outputs.ci-builder }},ethereumoptimism/ci-builder:latest