Fix env sourcing for CI test runner

GitLab CI runs each script line in a separate shell context, so sourcing
.env on one line doesn't carry to the next. Use export $(grep ...) on the
same line as jest to ensure DATABASE_URL is in the process environment.

.gitlab-ci.yml

@@ -105,8 +105,8 @@ test-backend:
     - npm ci --prefer-offline
     # Source backend .env from the production install so DATABASE_URL is available
     # for integration tests. Safe because the runner is on the same machine as the DB.
-    - set -a && source /home/cve-dashboard/backend/.env && set +a
-    - ./node_modules/.bin/jest --ci --forceExit backend/__tests__/
+    # Must be on same line as jest because each script line is a separate shell context.
+    - export $(grep -v '^#' /home/cve-dashboard/backend/.env | xargs) && ./node_modules/.bin/jest --ci --forceExit backend/__tests__/
   timeout: 5 minutes
   needs:
     - install-backend