Beaker Executor opens a ton of files

### 🐛 Describe the bug

You have to do this in a catwalk context, on commit `e7c5d158b9e8f1c925b4894037b5371a1efdeab7`.
```Python
from tango import StepGraph
sg = StepGraph.from_file("experiments/everything/everything.jsonnet")
from tango import Workspace
ws = Workspace.from_url("beaker://ai2/task-complexity")
s = sg['trained_model_sciq_bert-base-uncased_1337']
r = ws.step_result(s)
```
At this point the Beaker Workspace will open millions of files, quickly exhausting the open file limit. Even when you Ctrl+C the proceedings, background threads keep trying to open files. Your console is now useless.

### Versions

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