Add test for memory leak through StepExecutionIterator when build is stuck loading programPromise

[dwnusbaum]

Comparable to #347.

I ran into another similar memory leak, but unlike in the previous case where the problematic build was stuck in an infinite loop in its CpsVmExecutorService, in this case the problematic build's programPromise was stuck and never finished loading pickles because a FilePathPickle was looping forever.

This PR just adds a test to show that the fix in the previous PR handles memory leaks in both cases.

Testing done

Submitter checklist

• Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or Jira
• Link to relevant pull requests, esp. upstream and downstream changes
• Ensure you have provided tests - that demonstrates feature works or fixes the issue