Use cached app data in release/build-documentation

[aplowman]

Getting rate-limited otherwise. E.g. https://github.com/hpcflow/matflow/actions/runs/24244391900/job/70788405577

[dkfellows]

Be careful. We now delete that cache part way through the run to avoid hammering our storage quota quite so hard.