Auto merge of #24683 - servo:split, r=jdm
Auto merge of #24683 - servo:split, r=jdm

Split doc generation into its own task

This task reached its 60 minutes timeout in
https://community-tc.services.mozilla.com/tasks/YByC2V7uQq2lQv40TVi5KQ/runs/1/logs/live/https%3A%2F%2Fcommunity-tc.services.mozilla.com%2Fapi%2Fqueue%2Fv1%2Ftask%2FYByC2V7uQq2lQv40TVi5KQ%2Fruns%2F1%2Fartifacts%2Fpublic%2Flogs%2Flive.log#L6276

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