Specify the exact tag because latest is unavailable.

- Issue reported in aws/jsii#3505.
- Upstream https://hub.docker.com/r/jsii/superchain recommends the `1-bullseye-slim` version.

Author: Esen Sagynov

.github/workflows/build.yml

@@ -31,4 +31,4 @@ jobs:
       #- name: Anti-tamper check
       #  run: git diff --exit-code
     container:
-      image: jsii/superchain
+      image: jsii/superchain:1-bullseye-slim