ci(dependency-graph): remove packing artifacts from cache

.github/workflows/test-all-packages.yml

@@ -68,6 +68,12 @@ jobs:
       - name: Pack packages
         run: yarn lerna run --reject-cycles --concurrency 1 prepack
 
+      # Don't put the prepack artifacts in the cache maintained by restore-node,
+      # since they are not .gitignored and thus will fail restore-node's check
+      # for a clean repo when the cache is restored.
+      - name: Prevent caching prepack artifacts
+        run: yarn lerna run postpack
+
   ##################
   # Lint tests
   # We run per package bc of https://github.com/typescript-eslint/typescript-eslint/issues/1192