Clean up credentials file after E2E job.

[radeusgd]

Pull Request Description

• While Accessing and modifying description and labels of Enso Cloud assets #11255 fixes the root cause of Often random failures of Audit_Spec on the CI #11278, this PR fixes what triggered it - since Run integration in CI. #11198 our runners were keeping ~/.enso/credentials file between runs, meaning that some tests were unexpectedly running in 'authenticated' mode. This PR cleans up this file to avoid that.

Important Notes

Checklist

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• The documentation has been updated, if necessary.
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• Unit tests have been written where possible.