Bioconductor enumeration code is fault-intolerant

[Andrew Pollock]

Describe the bug
Bioconductor ecosystem test failures (due to the code under test being brittle) blocked unrelated PRs

Expected behaviour
A degree of intermittent non-200 responses shouldn't cause immediate enumeration failure

https://requests.readthedocs.io/en/latest/user/advanced/#example-automatic-retries

Additionally, during periods of external infrastructure failure, the tests could fail open.