bug(test-downstream-projects): shelljs prevents running on local machine

[aaron-brown]

This issue was identified in ui-router/angular-hybrid#612, specifically here.

-> yarn test:downstream --group-all

...

           ===> Moving working directory to temp dir /tmp/tmp-19274-QrHyqVsh55aM <===
mv: omitting directory '/home/.../ui-router/angular-hybrid/.downstream_cache'
mv: path is a directory
           ===> Running the following downstream tests <===
           ===> example                                <===
           ===> sample-app-angular-hybrid              <===
Error: ENOENT: no such file or directory, chdir '/home/.../ui-router/angular-hybrid' -> '/tmp/tmp-19274-QrHyqVsh55aM/.downstream_cache'
    at process.wrappedChdir [as chdir] (node:internal/bootstrap/switches/does_own_process_state:130:14)
    at runDownstreamTests (/home/.../ui-router/angular-hybrid/node_modules/@uirouter/publish-scripts/test_downstream_projects.js:250:11)
    at /home/.../ui-router/angular-hybrid/node_modules/@uirouter/publish-scripts/test_downstream_projects.js:339:3
    at Array.forEach (<anonymous>)
    at Object.<anonymous> (/home/.../ui-router/angular-hybrid/node_modules/@uirouter/publish-scripts/test_downstream_projects.js:338:28)
    at Module._compile (node:internal/modules/cjs/loader:1521:14)
    at Module._extensions..js (node:internal/modules/cjs/loader:1623:10)
    at Module.load (node:internal/modules/cjs/loader:1266:32)
    at Module._load (node:internal/modules/cjs/loader:1091:12)
    at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:164:12)
mv: no such file or directory: /tmp/tmp-19274-QrHyqVsh55aM/.downstream_cache
           ===> Successfully ran downstream tests for:  <===
           ===> Did not try to run downstream tests for: example, sample-app-angular-hybrid <===
error Command failed with exit code 1.

I attempted to reproduce it, but the Linux mv command was working normally / as expected.

This issue is a formality, and I will be submitting a PR to resolve this soon.