batches: remove ExecutionWorkspaces storybook flake
Created by: LawnGnome
We didn't have a mock set up for retrieving the changeset diff in
ExecutionWorkspaces, and the error message therefore included the host
name of the Chromatic instance that was running the storybook. (See
https://www.chromatic.com/pullrequest?appId=5f0f381c0e50750022dc6bf7&number=36331&view=changes
for an example.)
Test plan
Checked the storybook, which no longer has an error in it.
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