Run Jest tests in a single process

CircleCI tests run 8x slower than on my laptop (M2 Pro). Try the
suggested mitigation from https://jestjs.io/docs/troubleshooting

.circleci/config.yml

@@ -71,6 +71,7 @@ jobs:
             mkdir --parents /tmp/workspace/test-results/frontend-coverage
             npm test --workspace frontend -- \
               --ci \
+              --runInBand \
               --coverageDirectory=/tmp/workspace/test-results/frontend-coverage
       - store_test_results:
           path: frontend/junit.xml