bpo-30052: Always regenerate cross-references (GH-1339) (GH-1921)

bpo-30052: Always regenerate cross-references (GH-1339) (GH-1921)

The patch for bpo-30052 changed the preferred link target
for :func:`bytes` and :func`bytearray` references to be the
respective type definitions rather than the corresponding
builtin function entries.

This patch changes the daily documentation builds to disable
the output caching in Sphinx, in order to ensure that
cross-reference changes like this one are reliably picked
up and applied automatically after merging.
(cherry picked from commit 7a82f9c2b94d31c8f4cc8bb8e3151765d8b148d7)