Merge pull request #23755 from storybookjs/kasper/ci-flake

Build: Fix CI flakiness by setting TEST_ROOT for the test runner

Author: kasperpeulen

scripts/tasks/test-runner-build.ts

@@ -25,6 +25,7 @@ export const testRunnerBuild: Task & { port: number } = {
         ...execOptions,
         env: {
           JEST_JUNIT_OUTPUT_FILE: junitFilename,
+          TEST_ROOT: sandboxDir,
         },
       },
       { dryRun, debug }